Flatpak does respect your GTK+ Theme - but you have to either have it installed in ~/.local/share/themes or youbhave to download your theme as flatpak package a

Flatpak does respect your GTK+ Theme - but you have to either have it installed in ~/.local/share/themes or youbhave to download your theme as flatpak package aswell. But that implies that someone has to maintain the flatpak packge. While the most popular themes are available, more "niece" themes are missing. Do a `flatpak remote-ls flathub | grep --color "org.gtk.Gtk3theme"` to see all available themes. Note: I'm maintaining a theme on flathub.