Lauda89 Just an update..
I installed W11 with the latest updates and am using the 1660 SUPER with the DVI --> HDMI output of the monitor.
With the DVI output, the situation has improved, and it gets even better by setting limited RGB. Let's say that with DVI + limited RGB I can use the PC. It's not perfect because I can't stay relaxed, but for playing with it 2/3h is ok.
Unfortunately with this setting, the monitor colors suck and I am limited to 120hz (my monitor is 240hz).