Hi, I’m not sure if it has to do with my 3840 x 2160 screen, but all of my custom icons are pixelated, whereas the prepackaged icons are still perfect. imgur.com/a/IWb4vUZ
I haven’t messed around with custom icons at all, so can’t offer any specific suggestions, but I do know that there is a fairly detailed section in the manual about them. See 7.4 Custom Icons, particularly the section Tips for Sharp Icons, which discusses the best size to use for your .ico files.
Hopefully you find something useful in there. If you’ve already read that bit of the manual, then perhaps someone else with actual experience will come along and offer you real advice.