It is very much supported. Top left, click on your name, 'Add account', and go from there. I think in the backend the accounts might be associated for securit

It is very much supported. Top left, click on your name, 'Add account', and go from there. I think in the backend the accounts might be associated for security/abuse purposes, but Instagram actively wants you to be able to have more than one account. I'd imagine it would be a lot harder to avoid being 'thirsty on main' without these features. Just checked, and signed up with a random second account. They add the phone number from the previous account you were on by default, and mention copying your other non-public information over from the previous account you were signed in to.