alt Hacker NewsThose apps you mentioned are not your typical modern GTK4/libadwaita apps, so naturally you can theme them. It's the GTK4 apps - and ones which use libadwaita specifically - that cause grief.
- Firefox: Uses its own custom rendering engine but interfaces with GTK3. It respects standard GTK3 themes.
- Thunar: Uses GTK3
- GIMP: Since v3.0, they now use GTK3
- LibreOffice: Uses its own visual framework (VCL) but has a GTK3 plugin to draw its window frame and menus, and it also respects the system theme.
None of these use libadwaita, let alone GTK4, so they're not good examples unfortunately.
> so they're not good examples unfortunately
They're some of the most popular GTK apps available. They seems like a good example to me.
The themes I'm using are compatible with GTK4 apps too.
I use niri which suggests installing xdg-desktop-portal-gnome which comes with Nautilus which is a GTK4 app. It's perfectly themed just like the GTK3 apps.