Ican't change my gtk3 theme on manjaro 20.1 with kde plasma 5.19.5 and kde frameworks 5.74, my kernel is 5.8.11-1-MANJARO.
I have installed kde-gtk-config but when I start systemsettings and go to application style -> application style there is no change gtk theme button. I have also gnome installed and changed there the gtk theme but this don't worked on plasma.
Thanks to everyone answering.

Please observe http://bugs.kde.org/show_bug.cgi?id=450092 and assist if you are able to.