I have a 5K Retina iMac 2019 that was previously running on Catalina. I have a 1080p View Sonic monitor connected through a UBS port. I've been using a dual monitor set up for months now without an issue. I updated to macOS Big Sur and now the external monitor is not receiving a signal. When I go into my display settings, the Arrangement tab is missing. It seems after the update the 2 devices stopped communicating with each other. I've tried rebooting the iMac and the View Sonic, but I cannot get them to communicate. Has anyone else had this problem? Were you able to resolve it?