Hello. I released a new version of my theme changing app for Linux.
It adds the feature to (force) set the theme of gnome libadwaita apps without libadwaita patches, among other minor tweaks. Besides that, it can change GTK2/3/4, Kvantum, icon and cursor themes, GTK CSS and some appearance settings across GUI frameworks.
Hope this is useful.
Maybe you would be interested into maintaining Gradience instead of making a new LibAdwaita theming app from scratch ? Just thinking, haven't tested it but I don't see any straight reasons for one over the other outside the maintainership. https://github.com/GradienceTeam/Gradience