I first tried uninstalling the various Mixed Reality stuff from the Add/Remove apps panel and that didn’t fix my Windows update failure. Then I discovered the special option to uninstall Windows Mixed Reality in Settings (via a search) and that did allow my Windows update to complete successfully. (This after trying many times before and even downloading the updater separately and that still failing.)
Pretty ridiculous that you have to uninstall some Microsoft software to get a Windows update to conplete successfully. (And then there’s that stupid unhelpful error message.)