When attempting to mirror my display, both screens will go black, show the mouse on both monitors then revert back to the previous settings before asking me to confirm the changes. I am using Zorin os 16.2 Core. (Just got it to work but not sure why it doesn't work every time).
I usually see the complaint that the displays revert to mirrored, not the other way around.
Can you post the output of
sudo lshw -C video