While it’s not open world, I tried getting OSM data into SuperTuxKart a few years ago: https://wiki.openstreetmap.org/wiki/SuperTuxKart

It works, and it would probably look much better nowadays due to the progress of both the OSM tools and STK’s engine, but I never got around to polishing it to make it easy to produce your maps of your own city with this process.

There’s no doubt that there’s a lot of potential here. After all, even some commercial games like XPlane use OSM data quite heavily. But making it work well, and actually fun to play, is a lot of work even if one starts by modding an existing game. (I’ve always wondered whether one could build OSM-based maps for ETS2, for example. :))