If you’re moderately tech-inclined, its not super difficult to set up a streaming music server that you can access from anywhere. The most basic solution that almost anyone can spin up is a cheap NAS (or always-on PC), and setting up a VPN between your phone and router to access your library.

From there you can add complexity by configuring a true music server like Navidrome, adding web-facing access, erc

After typing this, I realized maybe you meant completely decoupling music from your phone, not just decoupling the storage