So on latest Plasma (on Testing branch), I still have the issue when waking up the computer with dual monitors where my primary monitor wouldn’t go back up and the second one would only show a black screen with mouse cursor (it can move it is not frozen but I can basically do nothing from there). After reboot the primary monitor is still not working but I can use the second monitor to open Nvidia panel and set up monitors properly.
Related issue Primary screen not working after wake from sleep (only KDE 5.26)
I think I will go back to Plasma LTS for now as this one issue is a deal breaker for me.