Comment 49 for bug 1849084

@Richard:

I tried your suggestion without luck. The screen remains black, the backlight was switched on. To verify I tried multiple times.

The only true workaround (with KDE) is to switch the compositor off before turning into sleep. You have to switch the compositor on after return from suspend. Somewhere I've found a systemctl script to manage this automatically, but I experienced the script's working not reliable.

With KDE you have to press Shift-Alt-F12 to toggle manually the compositor's state.

This is the output after returning from suspend with compositor switched off:

klaus@Lin:~$ sudo systemctl status plasma-restart@$USER.service
● <email address hidden> - Plasma Restart Service
   Loaded: loaded (/etc/systemd/system/plasma-restart@.service; indirect; vendor preset: enabled)
   Active: inactive (dead)

Mai 03 16:20:59 Lin systemd[1]: <email address hidden>: Unit not needed anymore. Stopping.
Mai 03 16:20:59 Lin systemd[1]: <email address hidden>: Failed to enqueue stop job, ignoring: Transaction is destructive.
Mai 03 16:20:59 Lin systemd[1]: Starting Plasma Restart Service...
Mai 03 16:20:59 Lin sudo[3652]: klaus : TTY=unknown ; PWD=/home/klaus ; USER=klaus ; COMMAND=/bin/bash -c pkill -ABRT plasmashell
Mai 03 16:20:59 Lin sudo[3652]: pam_unix(sudo:session): session opened for user klaus by (uid=0)
Mai 03 16:20:59 Lin sudo[3652]: pam_unix(sudo:session): session closed for user klaus
Mai 03 16:20:59 Lin systemd[1]: Started Plasma Restart Service.
Mai 03 16:20:59 Lin systemd[1]: <email address hidden>: Unit not needed anymore. Stopping.
Mai 03 16:20:59 Lin systemd[1]: Stopped Plasma Restart Service.

Something seems to be wrong, but I'm not the specialist for systemctl scripts.

Regards, Klaus