Shh...you're not supposed to mention these things alas you be down voted to death.
I also have tremendous issues with Plasma. Things such as graphics glitching in the alt+tab task switcher or Firefox choking the whole system when opening a single 4k PNG image. This is pre-alpha software... So back to X11 it is. Try again in another decade or two.
The thing is that I'm not experiencing this clipboard issue on Plasma, but on a fresh installation of Void Linux with niri. There are reports of this issue all over[1][2][3], so it's clearly not an isolated problem. The frustrating thing is that I wouldn't even know which project to report it to. What a clusterfuck.
I can't go back to X11 since the community is deliberately killing it. And relying on a fork maintained by a single person is insane to me.
[1]: https://old.reddit.com/r/hyprland/comments/1d4s9bw/ctrlc_ctr...
[2]: https://old.reddit.com/r/tuxedocomputers/comments/1i9v0n7/co...
[3]: https://old.reddit.com/r/kde/comments/1jl6zv7/why_does_copyp...
YMMV and all, but my experience is that Wayland smoothness varies considerably depending on hardware. On modernish Intel and AMD iGPUs for example I’ve not had much trouble with Wayland whereas my tower with an Nvidia 3000 series card was considerably more troublesome with it.