Pixelated Display on Ubuntu 20.04, using a Dell Inspiron 3585

So I installed 18.04 but nothing was working properly. Windows would randomly close themselves in the middle of doing a task. For example, I was running sudo apt upgrade and the terminal window simply closed. So was forced to install 20.04, which at least is useable, but now I have to contend with these boxes that appear on the screen, and disappear when I change windows, only to come back later