External monitor does not work with Macbook Pro M1 Pro

Hello Felix100facons,

With your MacBook Pro not displaying on your external monitor, we'd recommend reviewing the following steps: If your external display isn't detected or appears blurry when connected to your Mac - Apple Support

If your display is blank or not detected

Try these steps if you don't see an image on your display.

Check your cable or adapter

Disconnect the cable from your external display from your Mac, then reconnect it. If the cable from your external display doesn't connect to the ports on your Mac, you can use a USB-C or Thunderbolt adapter. If you're using a USB-C or Thunderbolt adapter to connect a display, the adapter must be compliant with DisplayPort Alt Mode or Thunderbolt / USB 4.

Check how many displays you can connect

If you're connecting multiple displays to your Mac, use the Tech Specs page to find out how many external displays your Mac supports.

Choose Apple menu  > About This Mac, double-click your serial number, then press Command-C to copy it.

Go to the Tech Specs page, click the Search Tech Specs bar, press Command-V to enter your computer's serial number, then click Search.

Click the specs page for your Mac. The number of displays your Mac supports appears under Video Support or Graphics.

Cheers!