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

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2024-04-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724931</rptOwnerCik>
            <rptOwnerName>Gebo Kate</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>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP HR and Labor Relations</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2024-04-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>15000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>50.861</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>57512</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2024-04-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>15000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>50.824</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>57512</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $50.85 to $50.89, inclusive. The reporting person undertakes to provide to United Airlines Holdings, Inc., any security holder of United Airlines Holdings, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this Form 4.</footnote>
        <footnote id="F2">Balance held in a revocable trust in the name of the reporting person.</footnote>
        <footnote id="F3">The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $50.81 to $50.85, inclusive. The reporting person undertakes to provide to United Airlines Holdings, Inc., any security holder of United Airlines Holdings, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this Form 4.</footnote>
        <footnote id="F4">By spouse of the reporting person.</footnote>
        <footnote id="F5">Balance held in a revocable trust in the name of the spouse of the reporting person.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ James Cotton for Kate Gebo</signatureName>
        <signatureDate>2024-04-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
[{"type": "4", "sequence": "1", "filename": "wk-form4_1713821571.xml", "description": "FORM 4", "secsgml_size_bytes": 6082}]
X0508
4
2024-04-18
0
0000100517
United Airlines Holdings, Inc.
UAL
0001724931
Gebo Kate
P. O. BOX 66100 HDQLD
CHICAGO
IL
60666
0
1
0
0
EVP HR and Labor Relations
0
Common Stock
2024-04-18
4
S
0
15000
50.861
D
57512
D
Common Stock
2024-04-18
4
S
0
15000
50.824
D
57512
I
See Footnote
The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $50.85 to $50.89, inclusive. The reporting person undertakes to provide to United Airlines Holdings, Inc., any security holder of United Airlines Holdings, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this Form 4.
Balance held in a revocable trust in the name of the reporting person.
The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $50.81 to $50.85, inclusive. The reporting person undertakes to provide to United Airlines Holdings, Inc., any security holder of United Airlines Holdings, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this Form 4.
By spouse of the reporting person.
Balance held in a revocable trust in the name of the spouse of the reporting person.
/s/ James Cotton for Kate Gebo
2024-04-22