Somehow we did it before spotify :). Browse forums. See what people are talking about. Follow local venues and see who is coming to town. Read about different artists. Different producers. Different record companies. Fall down the rabbit hole. You don’t need an algorithm to tell you what to listen to. Take the reigns. It’s a hobby right? Lean in.

This^.

There're recommendations in these comments that can solve the automating and downloading part of it but they still don't solve the discovery part of it.

The only way I see is - use Spotify to discover; sync your library using said software to collect and play later.

I do not know what you are listening to, but for my kind od music I have few webpages that I can visit for new and old releases. I can filter for example by genre and see few yt videos with to see if this is something I would like. Then you can download it or buy it. This is a lot od work but I would never discover few bands 'the spotify way'. Like i.e. Austrian Death Machine.