When you think about it, yes, it could be an entity that you need to be able to edit and that somehow also has dynamic fields and field types. I don't want to have to go in and predefine a bunch of field names.
If a meetup has SimpleX or Matrix invitation links, then it should be possible to simply add these to the entity.
And the creator must be able to change these links/values. Ideally, it should also be possible to delete the entity if the meetup no longer exists. Setting it to inactive is also acceptable.
I'll take a look at the suggestions I've received so far.