For running, I got a smartwatch that can store some music locally, so I don’t need to be connected to listen. Still not perfect, kind of a hassle to use, and doesn’t always work perfectly. Almost miss those tiny iPod nanos. I feel like portable dedicated music players have gone backwards in features and usability with the rise in popularity of perpetually connected Internet devices and streaming services.
The Samsung gear watches all support Spotify offline playback. All the wearOS watches support as much local media playback as the hardware allows (I think), but managing that local library is pretty tedious and awful. Especially if like me you either listen through streaming services or streaming from a library of FLAC media on a NAS at home. With the Spotify app on my watch, I just select a playlist to be downloaded while I’m connected to WiFi and that’s it. It is not flawless though, sometimes the Spotify database or authentication gets fouled up and you’re unable to fix it until you return to WiFi. But I haven’t had many issues with it since Samsung switched away from their own bespoke watch OS to wearOS.