Display problems

After the update to Mac OS Mojave version 10.14, every time I start my Mac mini (late 2012) I have to adjust the screen size. I do this by system preferences, display, then just clicking on underscan. It goes from an oversized screen, cutting off the top and bottom bar, to what should be the constant normal fitted screen size. This is quite annoying, so I was hoping somebody would have a solution for me!