Is it okay to add strangers on LinkedIn?

Question

Career in IT

I am actively looking for a job. On the advice of a friend, I decided to try Linkedin.
And a funny fact - he does not allow me to add friends, requiring a pro-account, but meanwhile offers a lot of people with whom I do not know - people who worked in the same companies, but in other offices, just people with whom I corresponded on various issues - from interviews, those. support, freelance orders. So I'm looking for a new job, on the one hand - it's reasonable to maximize the number of connections, but on the other hand, I don't remember them, they most likely me too.
Does it have any rules for adding each other in LinkedIn?
Still a professional network.