Confirmed working on 7.2.4 - I'm now able to start a Time Machine backup! 1.2% copied, let's see if it finishes! I wasn't able to get this far before on the older versions of Unraid. Thanks everyone, especially @JorgeB and LT! update: backup finished successfully. All working!
Is there any detail anywhere about this? I was hoping it would fix the "The backup disk image could not be created." error on MacOS Tahoe, but I'm getting the same error even after the upgrade.