I suspect that TDE's GTK3 theme engine is broken because of the radical changes the GTK developers have introduced, and has no further development at the moment (at least this is what seems to be happening). Thus, it must be only compatible with some very old versions of GTK3 (quite a pity because GTK3 is all over the place now as more and more apps drop GTK2 support).
I hope that this will be fixed some time in the future... For the moment I'd suggest using some sensible GTK3 theme or a GTK2 alternative.
-- Yours, Mavridis Philippe
13 Μαρ 2021 11:30:38 μ.μ. Jacob Alexander Tice <jacob.a.tice@gmail.com>:
On Ubuntu 20.10, GTK3 applications don't theme correctly. The menus are to small and selections aren't highlighted.