Apps would no longer display UI elements.
This is not a question, rather this is just a disclaimer for those who may be looking for it. Once I updated my HoloLens 2 to the Build 22621.1258 released this January, all of my Unity apps could no longer display UI elements. They were all working perfectly fine in every other aspect, except for the fact that they would not display UI elements. I tried several fixes, as this is an error that has plagued many HoloLens updates over the years, but none of them worked. Rolling back to the previous version (Dec. 2023 ver) with the recovery tool fixed the problem. Though I tried many version and using none of them fixed the issue, I was originally using Unity 2021.3.27f1.
It appears this is also resolved by the February 2024 update to 22621.1263, though they make no mention of it in the changelog.