Still no fixes here, even when trying to fix it from a Windows machine. I even managed to get a crash log I've never seen before, and it didn't lead to any new clues. (The log just said the material array had too many things in it, but changing that still crashes) Since I can't seem to figure out why Unity UI is causing issues, I've made an asset that completely replaces Unity UI and should be up on the Unity Asset Store shortly. If anyone in this thread wants a free copy for putting up w/ all this, let me know! I'll hopefully put it on itch shortly so I can distribute some keys.
Not exactly the best fix for the issue, but it is a workaround, and I don't see myself needing Unity UI for anything w/ this new asset.