Set GTK Theme based on the sun position
This was a bodge I used when Gnome 40 was released and forced all extensions to update their GUIs to GTK4 (which broke existing GTK3 ones). I was asked about it, so I set this repo to public. It was never intended to be used, but it might work out for you. Good luck!
Update: I adapted it to work with Gnome 42 and its color-scheme light/dark.
Normally I use the Gnome extension Night Theme Switcher which is also available in the (AUR). It works with Gnome 40 now.