For whatever reason org.gtk.Gtk3theme.Breeze-Dark was deprecated
The workaround listed here: https://github.com/flathub/org.gtk.Gtk3theme.Breeze
Is to run: flatpak override --user --filesystem=xdg-config/gtk-3.0:ro
However, that exposes a little extra if you have favorite places stored
I think it works if you only expose xdg-config/gtk-3.0/colors.css, xdg-config/gtk-3.0/gtk.css, and xdg-config/gtk-3.0/settings.ini
If an attacker gets access to your system, they will be able to ensure you can’t get rid of their access
It will persist across operating system installs
However, this requires them to get access first