Plex does alright at suggesting music from your own library, and also has some really nice DJ-like song transitions that are legitimately way better than any other track fades. However, Plex users have been frustrated with the company’s slow response to fixing long-standing bugs, and some of the features are paid. It’s also not open-source.
No idea if it can suggest music that isn’t in your library; I know that they integrate with Tidal though, so maybe if you have that it’ll also suggest stuff from Tidal?
I seem to be in the minority, but I’ve never had issues with it resetting my default browser.