I am currently using OpenSUSE Tumbleweed and I am torn between it and EndeavourOS (I do like CachyOS but prefer a more ‘pure’ Arch-based distro). The main problem that I have at the moment is the theming of some GTK apps such as Picard and GParted; in OpenSUSE Tumbleweed, they look just like Plasma apps but in EndeavourOS and CachyOS, the apps look like old Windows NT applications. I have tried looking Here but the problem is still there. Can anyone help?
Have a look at System Settings → Colours and Themes → Application Style → Configure GNOME/GTK application Styl;e and see if you can set it there. Some themes don’t have a GTK theme though.