Please, define exactly what "Upon their first entry to the room" means, as I doubt you are now tracking the list of users who ever entered any room since the beginning of time. Is this defined by being pingable, being in the "Frequently in room" list or it is really a new information you are going to store? What action exactly constitutes "entering" (just entering, posting a message etc) and more importantly how does the platform remember that I previously entered?
Tangentially how does this integrate with rooms in GALLERY mode? Does the user still get the prompt even if they can't speak in the room? Does the system check for "write" permission? This is relevant to decide if the "room notices" for gallery rooms should focus on how to request access, the actual room rules or both.