The only case in which x11 will be removed from your sessions list is if you don’t have kwin-x11 installed. The fix that people are talking about only stops you from having an unbootable session if you’ve already had kwin-x11 installed.
We are, in general, following the archlinux process of making Wayland the default behavior for KDE. This fix was only intended to prevent users from having a bricked (read: GUI-less) system.
If you want to keep/restore x11 functionality, you’ll have to install plasma-x11-session