Teamviewer is not active at this computer...

I use a Destkop PC and a laptop.
Both with Windows 10 and the latest updates.
Teamviewer also with the current version.

The laptop runs continuously in continuous operation.
The background programm on the laptop is running fine and there are no WLAN disconnections.
The laptop screen turns off after 15 minutes inactivity.
There is no quiescent or energy saving mode.
The WLAN is permanently activated and is not interrupted.
The background program on the laptop is working fine.
The laptop does not have a virus scanner, a deactivated Windows Defender and a disabled Windows firewall.

If the screen on the laptop is switched on, I can easily access the laptop with Teamviewer without any problems.

If the laptop screen is turned off after 15 minutes, i cannot connect with Teamviewer to it. (Error message: Teamviewer is not active on the laptop).

If I press the finger on the keyboard of the laptop, so the screen is switched back on, then Teamviewer works again.

Why I can't use Teamviewer at the laptop when the screen is off?
All energy saving programs are disabled.

Does somebody has any idea?

Greetings
Joerg