I'm on KDE Arch and switched about a week ago. I have an Nvidia card and went straight from x11 to Wayland plasma 6. It's definitely prettier and smoother, but it's absolutely not as stable. Idk if that's an Nvidia things, a Wayland thing, or a plasma 6 thing, but I definitely have fairly consistent display issues after switching. I have a btrfs snapshot from right before I updated that's at plasma 5, so I have a fallback if I want it. It's mostly just an inconvenience right now, so I'll probably just ride it out for a while and see if things improve.
It's definitely Wayland on Nvidia, I had the same issues, Element had a flickering black screen. Switching the default session from Wayland to X11 fixed all issues.
From my experience it happens with any XWayland window that fails to hit your display refresh rate. Makes programs such as vscode or element almost impossible to use on high Hz screens, as their max fps is locked to 60.