Make ubuntu for Raspberry Pi fill up your entire monitor screen:
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In the /media/puffin/system-boot/usercfg.txt file add this line:

disable_overscan=1

Then reboot if done from Pi, can also be edited from SD card on PC.

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Main source: https://ubuntu-mate.community/t/fixing-overscan-raspberry-pi/20053/2

Additonal Source: https://www.techcoil.com/blog/how-to-make-your-raspberry-pi-fill-up-your-entire-monitor-screen-by-disabling-overscan-in-raspbian-stretch/

Date Found: January 15th, 2021