Problems with my external monitor

[Mojo1019]

Hi guys,

three months ago I leaved my home to stay with my parents during the lockdown, leaving behind my external monitor (the complete setup is in my signature). Today I have returned to my home and I discovered that if I set the refresh rate of my external monitor to 144Hz from 120Hz in System Preferences -> Displays It suddenly turns back and the message "DisplayPort No Signal" appears. By the way the computer still detects the monitor and If I click around the black screen I can even manage to open some applications or windows. I will attach a video for a better explanation.
Also the clamshell mode doesn't work anymore! When I close the lid the same message "DisplayPort No Signal" but keyboard and mouse remain backlit.

The computer is a MacBook Pro 16 inch running MacOS 10.15.4.

Here is the video:

Thank you for your help!

EDIT: 10.15.5 update did't solve the problems

 

[albebaubles]

Have you tried resetting the SMC?

Reset the SMC of your Mac - Apple Support

The SMC is responsible for managing power on your Mac. Resetting it can resolve certain uncommon issues related to power or thermal management.

support.apple.com

 

[Mojo1019]

Have you tried resetting the SMC?

Reset the SMC of your Mac - Apple Support

The SMC is responsible for managing power on your Mac. Resetting it can resolve certain uncommon issues related to power or thermal management.

support.apple.com

Yes but without success. Also the PRAM reset didn't work...

EDIT: sometimes I also have this notification

I have restarted the computer many times but this pop-up keeps coming