KB5038575 update and dism fails

I have two, probably related problems.

I first noticed that my Windows Update was failing. I tried multiple times and got several different errors:

Cumulative Update for Windows 11 Insider Preview (10.0.26120.770) (KB5039314)
Install error - 0x800f0922

Windows 11 Insider Preview 10.0.26120.961 (ge_release)
Download error - 0x80246019

Cumulative Update for Windows 11 Insider Preview (10.0.26120.961) (KB5038575)
Install error - 0x800736b3

Windows 11 Insider Preview 10.0.26120.961 (ge_release)
Download error - 0x800706ba

Cumulative Update for Windows 11 Insider Preview (10.0.26120.961) (KB5038575)
Install error - 0x800706be

• pausing and restarting windows updates
• deleting update cache directories (windows/SoftwareDistribution and windows/system32/catroot2)
• deleting the c:\$WinREAgent directory
• shutting down all the third party services I could, including antivirus.
• numerous reboots
• ensuring my net connection was solid with no VPN
• ensuring there is plenty of free space on my system disk

• chkdsk C:      -> no errors
• sfc /scannow -> no errors
• dism.exe /online /cleanup-image /restorehealth

And there is where the second problem occurs. It showed:

Deployment Image Servicing and Management tool
Version: 10.0.26100.1

Image Version: 10.0.26120.751

[==========================100.0%==========================]
Error: 0x800f081f

The source files could not be found.
Use the "Source" option to specify the location of the files that are required to restore the feature.

So following suggestions I found online, I downloaded a Windows 11 ISO file and used that as the dism source:

dism /Online /Cleanup-Image /RestoreHealth /Source:WIM:J:\Sources\Install.wim:6 /LimitAccess

but the results were exactly the same.

I suspect the Windows ISO I downloaded didn't work as a source for dism because it's not the same version as I'm running, as I'm on the Dev channel of the Insider Program. There doesn't appear to be an ISO that will match my system.

It's quite likely that the corrupt windows image is the cause of the failing update.

I tried running an inplace update from the Windows ISO disk, but the "Keep personal files and apps" option is disabled because:

Your files, apps and settings can't be kept because current version of Windows might be installed in an unsupported directory or you're trying to install an older version of Windows

So other than reinstalling Windows from scratch and spending a week re-installing my apps, how can I repair my system?

My current system is:  Windows 11 Pro 24H2 build 26120.751