This is what my computer currently looks like. Does anyone have any suggestions on what I could do with the wires to make them look better (more uniform and subtle)? I looked into cable sleeves but I'm not really sure what I can do with them to improve the appearance. Would I just shove all the wires that are close to each other in a single sleeve and then plug them each back into the motherboard?

You could get angled connector adapters to slim it down a bit: https://www.amazon.com/24Pin-female-adapter-desktop-supply/dp/B07BJ2QHM4

FWIW, it already looks really neat to me Mine aren't nearly that neat and I thought I wasn't doing too bad.