My Music (MP3 Player / DAP) with Wifi Sync

I have Apple Music because my partner is big into Apple and wanted to get the bundle with Apple TV Plus. Support isn't great on Android but it works so whatever. Anyway, knowing it's not compatible (and never will be with Garmin watches) I have been uploading my old music collection and syncing with Garmin Express. This works okay but this just seems so cumbersome in 2022. I like that there are community apps that use wifi sync for podcasts like Playrun. I figured the concept is about the same for a MP3 player, or more accurately a DAP. The dream would be to make a running playlist on my phone (or a web app) that I can update now and then, and then just sync my watch with an IQ app. Surely there are some digital music hoarders not on Spotify out there. I understand this is a complicated problem as it involves a server of some sort, so that's likely why it doesn't exist. Has anyone else mused about this? Not seeing much in my searching..

This is a Garmin Forum so I don't expect it a reply like this, but please don't reply saying to just get an Apple Watch & an iPhone (lol)