The article in help center (https://support.zoom.us/hc/en-us/articles/206476313-Managing-breakout-rooms) does not specify the maximum number of total participants can be assigned into breakout rooms (only per room limit is showed in a table). So I thought it is up to the meeting capacity. However, during an event last week, I was trying to assign 500+ people into 50 rooms, yet it seems nothing happened when I clicked the “Open All Rooms” button after I assigned everyone a room number. There was no error message or anything. So I was not sure what was happening. It took me some time to figure out that, in order to make it work, I have to remove some of the rooms to keep the total number of assigned participants below a certain (unknown) limit.
During the breakout room assignment, there is no indication on how many people in total (or remaining) can be assigned into rooms, nor any error message. And the “Open All Rooms” button is still in blue and clickable. So hopefully there is a number showing how many people remaining can be assigned into breakout rooms, or at least grey out the button to make it unclickable once it reaches the limit. Otherwise, we have no idea when to stop adding people into rooms