Blender 5.0 got a theme overhaul, removing hundreds of options and
adding some more. While versioning was attempted to keep themes
looking as close as possible, some settings are impossible to guess
so they require manual editing.
Reset the theme to the default. Similarly to how it was done in other
major overhauls (2.80, 3.0).
Documentation and tools to migrate themes will be available at:
https://developer.blender.org/docs/release_notes/5.0/user_interface/
Pull Request: https://projects.blender.org/blender/blender/pulls/147637
829c6a7b98