gtk3, gtk4 (probably?) qt, qt in flatpak, gtk3 in flatpak, gtk4 in flatpak (probably)... I'm just not fighting it anymore
I'm very glad to see projects like libadapta as themable alternatives to the libadwaita dogma. I've painstakingly themed my desktop to look and feel like a cohesive, modernized NT 4 workstation and should seriously consider contributing to libadapta in anticipation of libadwaita coming to more and more programs.
I am very stubborn about my computer's GUI, but also hopeful the community can bring back theming where GNOME is dead set against it. If they can make WindowBlinds for modern Windows, the equivalent in Linux is definitely achievable.