Greetings,
Long time linux, first time EndeavourOS - and loving it! EndeavourOS experience is best out-of-box I’ve had for a new, or perhaps any, distro. KDE/Plasma DE just works on a “new” 2021 Razer Blade AMD 6900HX with “Latest” 3080Ti NVidia discrete GPU. Until I connected a second monitor 
My question is definitely Newbie, maybe better in Kernel & Hardware or Multimedia?
Seems like Second Monitor Lag Issues still persist using latest NVidia driver 535.54.03-1 with Plasma. Several second lag is totally unusable (on second monitor, laptop display is fine). Did notice jostling the mouse made the display “catch up” immediately - not a great workaround though.
nvidia-smi shows driver is loaded and I’ve tried most of the recommendations I’ve found in previous forum posts: Set Performance Max in nvidia-settings, sudo envycontrol -s nvidia, … Downgrading to 525.89.02 also seems not to work (anymore, the NVidia driver does not load). The only reliable workaround -still not a solution- I’ve found so far is to force exclusive use of the discrete/NVidia GPU in the BIOS.
One additional item of note is behavior under XFCE is different (same driver version, same kernel). There, I am able to get both monitors working and no lag with >sudo envycontrol -s nvidia (only, no BIOS over-ride required). Both DEs are X11-based so Wayland is likely not involved.
These types of issues are frustrating, any other suggestions on things to try would be welcome as I would like to spend some time with Plasma. Right now enjoying the more familiar XFCE and experimenting with i3.