Rémi Verschelde is a user on mastodon.gamedev.place. You can follow them or interact with them if you have an account anywhere in the fediverse. If you don't, you can sign up here.
Rémi Verschelde @akien

Hello Mastodonts! I'm looking for a platform where users could pin their location on a map and give some contact info (opt-in), to let fellow users find out about their neighbors and organize local communities and events.

I want it and using , bonus points if there are hosted instances of it available.

@akien had a look at umap ?
framacarte.org/fr/
github.com/umap-project/umap/
don't know about the user interface exactly what you look for but it's probably easy (for a webdev) to add a component on some page that get the info and fills the map ?
(beware GPRD though ... ;) )