Mac Mini M2 Pro not recognizing DisplayPort monitor

Mac Mini M2 Pro - 2nd monitor suddenly not recognized.

I have a Mac Mini M2 Pro 32MB, running the latest verion MacOS Tahoe 26.5.2.

Overnight, when nothing did change, my Mac does not recognize the 2nd identical monitor LG HDR 4K, the one via Display Port. The HDMI connected monitor functions perfectly well. I changed the cables and restarted several times. But teh Mac only connects the screen with HDMI. The Display Port connected screen is not found anymore. How to solve this mistery?