Check out these if you haven’t already:
https://wiki.openstreetmap.org
A nice thing to implement would be the ability for npubs to favourite/comment/review existing OSM POIs in addition to coordinates as implemented currently. You could review your favourite cafe, restaurant, etc. that already exists on the OSM database or your favourite place on a mountain (no OSM POI available). I expect this is already possible with the existing MapBox API if you didn’t want to switch over to a hosted OSM instance straight away.
In the future it could be possible to add POIs on OSM through Yondar. Let’s say the best Sushi place in your area doesn’t exist on the platform, you could raise an issue into OSM to add that place. This would benefit OSM and Yondar.