I have a Dell Laptop with hybrid GPU Intel + Geforce GTX 1050. WHen I use my notebook in full NVIDIA mode I have no problems but when I use in hybrid mode and connect a second monitor KDE starts lagging too much. When I disable the compositor the lag stops.
Operating System: KDE neon 5.21 KDE Plasma Version: 5.21.1 KDE Frameworks Version: 5.79.0 Qt Version: 5.15.2 Kernel Version: 5.4.0-66-generic OS Type: 64-bit Graphics Platform: X11 Processors: 12 × AMD Ryzen 5 2600X Six-Core Processor Memory: 47,1 GiB of RAM Graphics Processor: GeForce GTX 1070 Ti/PCIe/SSE2 Before 5.21 compositor on OpenGL2 & OpenGL3 was slow and laggy, like in-game low fps but without big jerks. Web-Page had issues with scrolling (was slow), dragging windows was with delay, input was with delay, KDE main menu navigation was with really big delay. With every native desktop notification PC performance became much worst and slowest than before. But transparency and animations works ok, so composer works. Because that I prefer to switch off composer property and working with the pure gui. I had only one Issue with App's windows without composer. It was that unexpectedly moving on top place after switching desktops. Even window has no focus. After 5.21 upgrade I got a lot of new issues with both modes: with composer and without. So without composer I got new problem - browsers and some windows starts caching render from previous stage. How it works: - Open Firefox with static (!) page. - Switch to another desktop. - Go back to previous desktop with FF. And now you can see that instead FF window here is a render from previous desktop. Also browser caching windows that staying in front of browser's window. So you can see dirt trace while moving windows in front of browser's window. Next event that trigger rerender/repaint in browser erase this traces and show browser's content. That's the main issue while composer is disabled. So, when composer enabled we have same problems that were in versions before 5.21 (laggs and slow) but much powerful. System is slovy and laggy, like never before. So this mode is absolutely useless now for me.
If you experience issues even without compositing, it seems like an issue in xorg or maybe even drivers.