There is some sort of compatibility issue with cross-platform play right now. Specifically, involving the switch.
I’m also having this issue but with LAN Worlds
Please remember to give a brief idea of what your bug is in your title instead of just saying: “the update is broken”, it’s too broad to understand. But this is a terrain generation bug. 1.21.60 made a few changes to terrain generation and sometimes when terrain generation gets changed, it can cause issues on older worlds due to different generation.
Or a resource pack
Are you using mods by chance?
This must be some type of rendering bug with armor_cutout and possibly other internal shader files.
Please remember to explain the issue in text and not just make your title a random statement
This isn’t a bug; this is completely intentional. Do not report false bug reports.