Because pronouns are such common parts of speech, and because there are a fixed number of pronouns, they come with their own built-in possessive forms.
Mine, Ours, Yours, His, Hers, Its, Theirs
Of these, “mine” and “his” are the easiest, and rarely show up with an errant apostrophe, while “its” rarely shows up without one. The confusion is partly due to “it’s” being a valid contraction of “it is.” So “it” can legally appear with a trailing ’s. You can test whether that apostrophe is correct by simply expanding the contraction. If the expanded contraction sounds wrong, then dump the apostrophe. This same trick can be used with “yours” and “theirs.”
It’s going to rain. -> It is going to rain. -> Yes! It’s coat was red. -> It is coat was red. -> No! Its coat was red -> Yes!
Note that there is no risk of confusion between the possessive “its” and the plural of “it,” because the plural of “it” is “they” or “them.”