Today I rewired the display and other components (which I wired wrong the first time) and tested the code I had modified. Unfortunately, it didn’t work. I thought the problem was the display (since the screen just flickered) so I found a tutorial to just show a heart icon on the screen. Watched it, coded it in Arduino IDE and put it on the board. The display worked fine, except for a few rows which were very dim because I used too high a resistor. After I fixed that, I tried a few other small fixes, but no dice. I think that I’ll try to find a decent tutorial using a different kind of LED matrix and try to modify that instead.