I can confirm @kovacslt’s and @berninghausen’s observations:
Copy & paste works perfectly fine, with shortcut or select+middle-button between all kinds of apps and any given product of the LibreOffice suite, at least on KDE.
I didn’t try gedit, though, but with kate and VS Code - no problem.
As far as I can remember, this has always been the case, even when it was still OpenOffice.