There is an issue with darktable (thanks for reporting), doesn't start at all here, running from cli it shows:
[imageio_load_module_format] failed to open `avif': (null)
So far no luck in debugging, rebuild of libavif & rebuild of darktable itself presented no fix.
If no solution found soon, then a downgrade will be build. Since you mention a few months ago no issue, so I presume this started with 4.2.0.
Issue is in libavif & darktable, a rebuild version of darktable is up in the build repo, with libavif disabled, that version runs again.
You can try with:
sudo pacman -U http://kaosx.tk/repo/build/darktable-4.2.0-3-x86_64.pkg.tar.zst