SUMMARY
At random moments, but very frequently (more than half of the cases), the monitors remain black when trying to wake up the laptop (there is a signal, but nothing is displayed).
The settings are as follows:
- primary monitor - external
- laptop monitor is disabled
- when closing the laptop lid, don't turn it off, for use as a PC with an external monitor
- laptop 100% of time connected to electricity 

STEPS TO REPRODUCE
1. Just wait to sleep or logout manually 
2. Press power to wake up / turn on

OBSERVED RESULT
50-70% of cases I see black filled rect on both screens. Keyboard is lighting like laptop turned on but I don't see anything on the screen. 
Other 50-30% I see laptop's monitor blinks one time showing me lock screen. Then KDE understand that I turned this monitor off and switched to external. Looks bad, but tolerable, as for Linux distributive.
If reconnect external monitor, sometimes it helps and login screen appears on the laptop screen (turned off in the settings, lol)

EXPECTED RESULT
I expect my settings will be taken into account and after turning on I should see login screen on the my external monitor without any bugs and blinks.
Now it looks like all KDE devs using one monitor 😄 Because I tried it several years ago with different laptop and monitor and also faced with similar problems on X11. Now in 2025 with Wayland nothing changed. Using external monitor it's pain. I restarting my laptop almost every time when it sleeps.

SOFTWARE/OS VERSIONS
Reproduces on latest stable and latest testing packages.

Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: