Hello Daniel,
Thanks for reaching out!
There are 2 possibilities to have RSVPs for community submitted events.
1. Add an RSVP in the back-end after an event has been submitted – plugins required: The Events Calendar, Event Tickets and Community Events
2. Create it on the community events submission form – plugins required: the above and Community Tickets, Event Tickets Plus, WooCommerce.
Hope this helps. Let me know if you have any further questions.
Cheers,
Andras