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

Really? There’s something appealing to me about decoupling my cellular modem from my phone; I used an iPod Touch instead of a smartphone for years (with Wifi and VoIP).

At this point I have zero interest in a dedicated audio player.

And if I wanted one… my watch holds more MP3s than the original iPod did. I can just play music from my watch.

Or my graphing calculator.

Or, for that matter, my over the ear headphones which have a microSD slot.