Invitation user interface PS5

Hello, have 2 questions about invites on ps5:

  1. Why some people from my friend list can join my game without invitation and some need invitation? The same, i see some game after pressing PS button and can join some of them.
  2. Is it possible to invite people in game without adding them to friend list? Sometimes i make trades and people write me in discord, that they invited me, but i don’t see invitation. After they adding me as friend, i can see their invites. Maybe there are some options or privacy setting, which i need change?
    Thank you