Good morning John and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
I would love to help you with this topic.
At this point, this feature is not built-in.
The good news is that you can totally vote for it here: https://tribe.uservoice.com/forums/195723-feature-ideas/suggestions/6095921-add-waitlist-capability
The other good news from that same page is that as a temporary workaround, some people have suggested adding another RSVP ticket to your event called “waiting list” after the original ticket has sold out.
It is not perfect, but it might help.
Finally, if you are pressed for time, you might consider hiring one of our recommended customizers to do the customization for you.
Let me know if that helps.
Have a great day!
Geoff B.