Well this is linux. There is a choice of kits to develop UI. Some use GTK (with X subversions), some QT (with X subversions), some KDE (with X subversions), and then there are some that does not use them at all and make their own thing, like tigervnc client.
You can try to unify things in Appearance (GTK3), Kvantum and QT5 Settings. And that leaves only the GTK4 apps. For them you can somewhat remedy that with a config file. Not perfect, but better that nothing.