Basically at my wit's end with this one. I've tried remaking the answer file from scratch, ensuring it's being written properly to the .xml file, googled, asked chatGPT, etc. I don't know what else to check since it all literally hinges on the 'OnError' flag being respected entirely, regardless of any other setup steps.

Right now I have to have two answer files based on this conditional and just use the other one when it errors on disk config, but I'd really like to not have to do that.

<?xml version="1.0" encoding="utf-8"?>
<unattend xmlns="urn:schemas-microsoft-com:unattend">
    <settings pass="windowsPE">
        <component name="Microsoft-Windows-Setup" processorArchitecture="amd64" publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
            <DiskConfiguration>
                <WillShowUI>OnError</WillShowUI>
                <Disk wcm:action="add">
                    <DiskID>0</DiskID>
                    <WillWipeDisk>true</WillWipeDisk>
                    <CreatePartitions>
                        <CreatePartition wcm:action="add">
                            <Order>1</Order>
                            <Size>500</Size>
                            <Type>Primary</Type>
                            <Extend>false</Extend>
                        </CreatePartition>
                        <CreatePartition wcm:action="add">
                            <Order>2</Order>
                            <Size>100</Size>
                            <Type>EFI</Type>
                            <Extend>false</Extend>
                        </CreatePartition>
                        <CreatePartition wcm:action="add">
                            <Order>3</Order>
                            <Size>16</Size>
                            <Type>MSR</Type>
                            <Extend>false</Extend>
                        </CreatePartition>
                        <CreatePartition wcm:action="add">
                            <Order>4</Order>
                            <Type>Primary</Type>
                            <Extend>true</Extend>
                        </CreatePartition>
                    </CreatePartitions>
                    <ModifyPartitions>
                        <ModifyPartition wcm:action="add">
                            <Format>NTFS</Format>
                            <Label>WinRE</Label>
                            <Order>1</Order>
                            <PartitionID>1</PartitionID>
                        </ModifyPartition>
                        <ModifyPartition wcm:action="add">
                            <Order>2</Order>
                            <PartitionID>2</PartitionID>
                        </ModifyPartition>
                        <ModifyPartition wcm:action="add">
                            <Order>3</Order>
                            <PartitionID>3</PartitionID>
                        </ModifyPartition>
                        <ModifyPartition wcm:action="add">
                            <Format>NTFS</Format>
                            <Label>Windows</Label>
                            <Letter>C</Letter>
                            <Order>4</Order>
                            <PartitionID>4</PartitionID>
                        </ModifyPartition>
                    </ModifyPartitions>
                </Disk>
            </DiskConfiguration>
            <UserData>
                <ProductKey>
                    <Key>VK7JG-NPHTM-C97JM-9MPGT-3V66T</Key>
                </ProductKey>
            </UserData>
            <WindowsDeploymentServices>
                <Login>
                    <Credentials>
                        <Domain>blah</Domain>
                        <Password>blah</Password>
                        <Username>blah</Username>
                    </Credentials>
                </Login>
                <ImageSelection>
                    <InstallImage>
                        <Filename>install.wim</Filename>
                        <ImageGroup>Windows</ImageGroup>
                        <ImageName>Windows 11</ImageName>
                    </InstallImage>
                    <InstallTo>
                        <DiskID>0</DiskID>
                        <PartitionID>4</PartitionID>
                    </InstallTo>
                </ImageSelection>
            </WindowsDeploymentServices>
        </component>
        <component name="Microsoft-Windows-International-Core-WinPE" processorArchitecture="amd64" publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
            <SetupUILanguage>
                <UILanguage>en-US</UILanguage>
            </SetupUILanguage>
            <InputLocale>en-US</InputLocale>
            <SystemLocale>en-US</SystemLocale>
            <UILanguage>en-US</UILanguage>
            <UserLocale>en-US</UserLocale>
        </component>
    </settings>
    <cpi:offlineImage cpi:source="wim:d:/dev/.images/w11-golden/sources/install.wim#W11 Golden" xmlns:cpi="urn:schemas-microsoft-com:cpi" />
</unattend>

Pastebin to setupact.log

Either I get the setup to get to the disk config stage and then do nothing, or it'll error when it gets there. I really don't even know.