alcohol and things like that can loosen it all up, but look for Rapid Remover. it’s used in my printshop as a way to remove vinyl adhesive clue that’s left on. more than probably what your smaller stickers and decals leave. :p dunno where you can buy it, but be sure to have something like a spatula to get under the gunk once it’s loose.
then just scrape it all lose and you should be good. give it a nice shine once you’re done. ;D
if you’ve never tried it before, you should: LIGHTER FLUID
I work at a retail store that puts stickers on its window displays, and to wash off the residue after peeling stickers, we put lighter fluid straight onto the paper towel and then wipe… works perfectly and leaves no streaks
A household fix I’ve used to remove sticker goo is nail polish remover. I recommend double checking to make sure it doesn’t melt the cover though before dousing your mac in it.