Soulseek is the only "FOSS" solution. It's literally piracy though. There's no real free or open source way of getting licensed music. That's the whole point of copyright and royalties.
I buy physical media (CD, vinyl, cassette). The CDs get ripped to flac and I use Soulseek to download flac versions the of vinyl and cassettes. I listen to the physical copies at home and use Plex/Plexamp when I'm out.
The Nicotine+ client is FOSS, the Soulseek network is not though. Just a clarification. It's still the only relatively widely used means of obtaining music besides torrents, even though people can share any kind of files, not just audio ones.
With FOSS, self-hosted, Subsonic-compatible music media servers like Navidrome, one can build a streaming-site alternatuve with one's own collection.