Funny enough, Tim Connors and I just held a ~50 person event (this one was virtual, but have done both virtual and in-person) using a topic guided small group format.

Create a handful of interesting topics (hard, but not impossible), ~1 per 10 attendees and have people self-select into groups and discuss the topic.

EX. We had "How to use VC/PE/etc. playbooks to design a better nonprofit" and "ChatGPT: what's useful and what's hype?"

Have held these 5 times and they get rave reviews.