It's out there on youtube, but where can I buy the soundtrack for offline not-while-in-game listening?

Raft Original Soundtrack by Jannik Schmidt should be available on Spotify, Apple Music, Youtube Music and most other popular music platforms since December 2023. Here they are on Spotify and Youtube:

https://open.spotify.com/artist/4N6pCKvIMhLLOZIqo0zEHV