(Disclaimer: this relates to the commercial project I run, but it is directly answering the parent)

It's not self hosted, more a middle-ground between rented Spotify and self hosted data sovereignty, but this is what we do at https://asti.ga . You store your music in some Internet-accessible storage, such as any S3 compatible endpoint, and Astiga connects and streams your library (and provides offline etc etc). AMA.

Very relevant to my interest, thank you for posting, I wouldn't have found you otherwise.