For all other words you do 's to indicate possession

Only if the words are nouns, not for pronouns. "Its" is a possessive pronoun, like his, hers, ours, yours, theirs. None of those words use apostrophes.

Specifically because it conflicts with the contraction "it's", at least that's how I remember.

it's interesting how non-native speakers almost never confuse those though

we make other kinds of mistakes, personally i really struggle with prepositions in every one of my non-native languages, because my native language doesn't have them, but has a weird suffix system instead