As someone who has worked with this sort of stuff quite a bit, I can assure you that OSM is pretty terrible for Geocoding and reverse geocoding. OSM is great for all kinds of roads (everything from the largest highways to the tiniest unofficial hiking trails), pretty good for landuse and absolutely terrible for building footprints and addresses. In many countries you don't have to get far outside of major cities before half the buildings are just missing, and even the buildings that do exist very often have the wrong address or house number.

That's just not the case.

For a good geocoder, you need many other data sources (which can be open). OpenAddresses (https://openaddresses.io/) is an example of a vital dataset to delivering anything of any quality.

Returning real results requires extensive parsing and awareness of addresses and place data (including localization of them), and this is not something you get for free based on OSM data.

My experience is also that (in the uk at least) it can't be done accurately with openstreetmap data.

For context, I've tried it! I've been working on a free library for geocoding UK addresses quickly and accurately. It comes with the caveat that you need access to the dataset of all addresses you're geocoding against - which could be your own list, or a commercial product like addressbase: https://github.com/robinL/uk_address_matcher/