Black Screen during work Nvidia GeForce RTX 3060

[Andre]

Black Screen !!!not during Boot!!! !!!during Work!!!
1)
New lap top and new installation of Ubuntu 20.04.3 lts
2)
apt-cache policy pkgname is not working; Pkgconf? > Version table: 1.6.3-5 500

Hardware:
Dell XPS17 with Intel Core i9
GPU Nvidia GeForce RTX 3060 incl Driver installed.

description:
From Time to Time I end up in a black screen during my work.
it happens during Writing, using the mouse....
No specific running Software.

Again: It happens during my Work! it is not the Screen safer. It is maybe related to the screen safer. The screen safer usually don't start during work.

then I can not log in again.
When I close the Laptop and open it again, usually the Login Screens pop up again.
If I wait eg. one Hour and I move the mouse, the Login Screen pop up again.

I did not fond something in the syslog.
Tail -f syslog will not work; > black screen

I can not open a other TTY.

any advice where to find some detailed Error messages in log files?

Tryed to find something in the Internet > nothing.

3)
it should not happen.
4)
see description.

Thanks for Support