Same for the 5th, Brazil. Everyone uses WhatsApp here and has been more than a decade since the last time I've ever had to use sms (never even used mms).
Depends on what you plan on use when you do make a switch. In general, X applications will keep using Xdefaults because they run on XWayland, and the window manager will handle input configuration, displays, wallpaper and so on.
There are some ad-hoc implementations for doing what you want iirc, but it really is more "integrated" than what you are used for.
I have to test, have not done that in quite a while, but I think that you can just call let's say "sway" on the CLI and it will start wayland directly.