HeySummit does not create or limit breakout rooms itself. Your talk uses its connected video or webinar provider, so the number of concurrent breakout rooms and participants is set by that provider.
Check these limits before your event
Whether you are using a meeting or webinar product.
Your provider account, licence, and any capacity add-ons.
The total participant capacity and the number of people allowed in breakout rooms.
Whether breakout rooms are enabled for the host account.
Zoom example
Zoom currently documents up to 100 breakout rooms for meetings, with participant capacity depending on the meeting licence and add-ons. Zoom webinar breakout rooms use different limits and licence requirements. Check Zoom's current guidance for meeting breakout rooms and webinar breakout rooms before planning your session.
These are provider limits, not HeySummit limits, and providers may change them.