Update: when waking up after sleeping/suspending, I only see a black screen. To make things work:
- Disconnect external monitor and wait for some seconds till I see something in the laptop’s monitor.
- Login using the laptop monitor.
- Reconnect the external monitor.
- Plasma?/Kwin? crashes. It restarts on its own after a minute.
I think I’ll be forced to move to Wayland and adapt my workflow. I hope no other problems appear.