The meetup app still exists.
The reason for the decline in social activity is not that it was insufficiently commercialized. Meetup should be a nonprofit.
I still host board game events on Meetup, although I'm hoping to switch to my open source alternative soon. I think the other commercial options such as Discord and Facebook are worse, and people have gotten used to Meetup.
EDIT: Would it happen to be Meetable? I just stumbled across that serendipitously an hour or so after commenting.
Here are more details about the planned architecture: https://createthirdplaces.org/events/techOverview