Black border around display, Mate 16.04

I have a black boarder around my display. I tried to use Display options but Mate doesn't recognize my display. I then tried raspi-config and said no to Overscan, still no joy. What next?

I suggest investigating the display options-

  1. what are you using, and does it say what its native mode is anywhere?
  2. have you access to tvservice in a terminal, and if so what does tvservice -s show?

I am in the middle of a reinstallation to see if it was a bad installation. I will check again as soon as it finishes. Thanks.

Here is the screenshot of tvservice -s and the second shot boot/config.txt.

So far, so good but
You haven't said what device is used for display, and whether you still have the windowed effect

It is an Asus HDMi 27" LED display. It works fine with my Raspberry Pi 4B and Mate 20.10. Just not on 16 or 18 Mate.

I'm afraid that, at this point, I'd say there were too many oddities to find anything - could be in the various updates in Mate and how it uses RPI to display.