I've been thinking the same, so i built https://hollr.at. it's a PWA and probably alpha/beta quality at this point, being a side project. It works pretty good for me at least and others not familiar with it can join and attend without an account which seems to be appreciated. There is no stickiness or discovery to it though.

Apart from meetup.com I'd say that eventbrite.com looks pretty good. There is also https://mobilizon.org/en/ which seems to be federated, so you have the option to self host