Imac says ethernet is unplugged

I have an Imac (late 2014, 27-inch) and just updated to Catalina ver 10.15.6, and it says ethernet unplugged, which is not. In the previous version of ios internet via ethernet worked well and continuously. I have rebooted the modem, but no change. My wife runs an earlier version of Catalina and her internet runs fine. Appears that ios update messed things up. Need steps on how to regain internet/ethernet use. Running wireless at 2.4g.

Help