https://bugzilla.kernel.org/show_bug.cgi?id=202873
--- Comment #3 from Thomas (v10lator@myway.de) --- Now I just realized that I have a second display (TV - Samsung UE40H5090 - AFAIK also no FreeSync) attached and turned it on to see what happens: Both displays flicker. If I disable the second screen in LXQTs settings the flickering stops and all is fine.