Support for GTK 4 themes?

You can by granting your Flatpak the access to your .themes folder and your GTK4 config folder.

sudo flatpak override --filesystem=$HOME/.themes:ro
sudo flatpak override --filesystem=xdg-config/gtk-4.0:ro
sudo flatpak override --env GTK_THEME=[theme name]

(The theme need to be installed in .themes)