In general, if you’d like to organize a Nextcloud meetup - go do it!
There are few rules, the main one being “don’t abuse our name and avoid confusing people”.
Check the "Advocacy groups" section on Nextcloud trademark guidelines for details, but in short, you can use our name and logo, if you are genuinely organizing the event in a non-commercial, volunteer way, and make clear that you do this on your own accord and not on behalf of Nextcloud-the-company. That doesn’t mean you can’t find some sponsorship for food & drinks, but the goal of the event shouldn’t be to sell anything, and that should be clear to everyone.
With that out of the way, you can organize watch parties for releases, just drinks in a pub, or a full monthly meetup with casual conversation or even talks. Let us know here - create a topic to invite people, and let us know what you’re up to!