I have 2 computers with KDE which I've been using for the past 6 months or so. I recently read about how to switch to Wayland (log out, find the option, log back in). Both of my computers were using X11, not sure why. Maybe I chose that during installation.
I switched both to Wayland and I'm going to do my best to stick to it. One of my computers has an older Nvidia card but luckily I don't seem to have any problems.
Purely anecdotal, but maybe a large part of the 27% using X11 don't even know the difference.