Honestly I’ve done mostly forgot, and with the proliferation of AI technologies and all the typos AI has read from in the training models, I bet AI isn’t always right about this either.
I usually just don’t care anymore, whether the autocorrect puts the apostrophe in or not.
Apostrophe is only ever possessive when used with a noun.
Example:
“There was a stick in the dog’s mouth” <- correct, dog is a noun
The word “its” is not a noun, Instead it serves the same function of possessive pronouns like “his” or “hers” and like those words it is never in this usage written with an apostrophe:
“The dog had a stick in his mouth” <–correct
“The dog had a stick in its mouth” <-- correct
“The dog had a stick in it’s mouth” <-- wrong
In short, the ONLY rule you need to remember is that if the word “its” is short for “it is” then it should have an apostrophe, otherwise it doesn’t.
That’s all. One single rule, zero exceptions.
Then why does it vs it’s break all the other rules of the apostrophe?
Where’s the exact exception?
While it may seem like “it” and “it’s” are different forms of the same word, in reality they are completely different words
he / his
her / hers
It / its
The above are all different forms of the same words.
“it’s” however is merely a shortening of “it is” and on that basis is a totally different word that (very misleadingly!) happens to sound exactly the same as “its”
EDIT:
Another way of looking at this :)
his & he’s (shortening of “he is”) are different words in the same way, but nobody makes the mistake of writing or saying “he’s car” instead of “his car” - it’s obviously wrong because the words sound different - ‘hiz’ and ‘heez’
The same is exactly and identically true of “its” and “it’s’” but those words sound the same, so the mistake comes easily.
Don’t demand nitpicky references in triplicate from people who assumed you just wanted to know and didn’t understand you were out to normalize failing.
Go find a teacher. It’s that person’s job to show you why. If you don’t believe that person, then it’s an oppositional disorder you’ll need information on.