<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-05-22</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000100517</issuerCik>
        <issuerName>United Airlines Holdings, Inc.</issuerName>
        <issuerTradingSymbol>UAL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001292272</rptOwnerCik>
            <rptOwnerName>Whitehurst James M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>P. O. BOX 66100 HDQLD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60666</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-05-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3459</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>19417</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-05-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1730</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>74.60</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17687</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Share Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
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            <transactionDate>
                <value>2025-05-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2410</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2026-05-22</value>
            </exerciseDate>
            <expirationDate>
                <value>2026-05-22</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2410</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2410</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Share Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
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            <transactionDate>
                <value>2025-05-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3459</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2025-05-23</value>
            </exerciseDate>
            <expirationDate>
                <value>2025-05-23</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3459</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each share unit was the economic equivalent of one share of common stock. Upon vesting, the share units were settled (i) 50% in cash based on average of the high and low sale prices of a share of the Company's common stock on the vesting date (or the average of the high and low sale prices of the common stock on the preceding trading day if the vesting date is not a trading day) and (ii) 50% in shares of the Company's common stock, with any odd or fractional units rounded toward the share units to be settled in cash.</footnote>
        <footnote id="F2">Each share unit represents the economic equivalent of one share of common stock. Upon vesting, the share units are settled (i) 50% in cash based on average of the high and low sale prices of a share of the Company's common stock on the vesting date (or the average of the high and low sale prices of the common stock on the preceding trading day if the vesting date is not a trading day) and (ii) 50% in shares of the Company's common stock, with any odd or fractional units rounded toward the share units to be settled in cash.</footnote>
        <footnote id="F3">Additional share units accrue when and as dividends are paid on the Company's common stock. The number of share units accrued will be equal to the dollar amount of dividends that would be payable if the share units were actual shares of common stock, divided by the average of the high and low sale prices of a share of the Company's common stock on the date dividends are paid.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ James Cotton for James M. Whitehurst</signatureName>
        <signatureDate>2025-05-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0508
4
2025-05-22
0
0000100517
United Airlines Holdings, Inc.
UAL
0001292272
Whitehurst James M
P. O. BOX 66100 HDQLD
CHICAGO
IL
60666
1
0
0
0
0
Common Stock
2025-05-23
4
M
0
3459
A
19417
D
Common Stock
2025-05-23
4
D
0
1730
74.60
D
17687
D
Share Units
2025-05-22
4
A
0
2410
0
A
2026-05-22
2026-05-22
Common Stock
2410
2410
D
Share Units
2025-05-23
4
M
0
3459
D
2025-05-23
2025-05-23
Common Stock
3459
0
D
Each share unit was the economic equivalent of one share of common stock. Upon vesting, the share units were settled (i) 50% in cash based on average of the high and low sale prices of a share of the Company's common stock on the vesting date (or the average of the high and low sale prices of the common stock on the preceding trading day if the vesting date is not a trading day) and (ii) 50% in shares of the Company's common stock, with any odd or fractional units rounded toward the share units to be settled in cash.
Each share unit represents the economic equivalent of one share of common stock. Upon vesting, the share units are settled (i) 50% in cash based on average of the high and low sale prices of a share of the Company's common stock on the vesting date (or the average of the high and low sale prices of the common stock on the preceding trading day if the vesting date is not a trading day) and (ii) 50% in shares of the Company's common stock, with any odd or fractional units rounded toward the share units to be settled in cash.
Additional share units accrue when and as dividends are paid on the Company's common stock. The number of share units accrued will be equal to the dollar amount of dividends that would be payable if the share units were actual shares of common stock, divided by the average of the high and low sale prices of a share of the Company's common stock on the date dividends are paid.
/s/ James Cotton for James M. Whitehurst
2025-05-27