iMac not detecting external display

Hi,

My iMac 27" (2019 version) can't detect the external display (hp 27" 2K monitor) after an accidental power shut down (I accidentally unplug the power).

After the reboot, everything is find, except that the iMac can't detect the monitor anymore. I've changed the monitor, the same. I've attached the HP monitor to my macbook, it worked too. So it's not the minitor's issue.

I've also recently updated the MacOS to Catalina, just in case there is any connection there. But right after the OS update, I could still use the external monitor. So probably not related.

Please help me! thanks