There is a need for desktop border adjustment to fit the monitor screen before installation of any OS.
When I installed Ubuntu MATE 20.04 on Raspberry Pi 4 (4GB RAM), there was over-scan left, right, top and bottom. The top and bottom panels were not visible. Only the right half of the Main Menu was visible. When windows were displayed full screen, the title bar minimize, maximize and close buttons were not visible.
I managed to edit /boot/firmware/usercfg.txt in situ to correct the overscan, but this would be beyond the capability of a new computer user.
Ubuntu MATE 20.04 is great on RasPi 4, except for the above!
I must admit I had the same experience with Raspbian (now Raspberry Pi OS).
This is usually a problem with a particular Monitor/TV/Projector - most people have no trouble and don't need any such adjustment.
Derek