Have you checked ProtonDB? https://www.protondb.com/app/2623190 It's okay if you haven't, less people than I'd expect know about it.
I see this here from a month ago:
Tinker Steps:Switch to experimental, Changed configuration
Issue
After the update from 1.1 to 1.2, the game would crash with Unreal Engine 5 errors after the initial shader cache loading.
LowLevelFatalError -- Bad export index … WBP_Modern_CharacterCreation_EditableText_C
Happens after Bethesda’s update due to mismatched Unreal 5 caches and corrupted .pak files left behind by Steam in the shader caches and games compatdata directory.
Fix
Uninstalled the game.
Remove all leftover files
Reinstall game
rm -rf ~/.steam/root/steamapps/compatdata/2623190
rm -rf ~/.steam/root/steamapps/shadercache/2623190
rm -rf ~/.steam/steam/steamapps/compatdata/2623190
rm -rf ~/.steam/steam/steamapps/common/"Oblivion Remastered"
rm -rf ~/.steam/steam/steamapps/shadercache/2623190
rm -rf ~/.cache/OblivionRemastered ~/.cache/unreal*
Clear out the unreal engine cache
rm -rf ~/.cache/OblivionRemastered
rm -rf ~/.cache/unreal*
rm -rf ~/.cache/mesa_shader_cache
Graphics:Minor Artifacts
Performance:Slight Performance Problems
Poorly optmized game. Engine.ini tweaks and performance tweaking is required.