Yeah, it's an X thing. But on X, the highlight/middle-click clipboard is separate from the ctrl-c/ctrl-v clipboard, so you can hold two things at once when moving text around. IIRC this was just a historical quirk rather than any intentional design, and I think in Wayland they duplicated the controls but also combined them into a single clipboard.

Works on Wayland. Doesn't work in some assclown programs; e.g. claude attempts its own copy-to-clipboard feature, which goes around primary.