I wish I could do this but I have yet to find a good Apple Watch replacement for owning and syncing music (rather than streaming it) Is it not possible to sync

I wish I could do this but I have yet to find a good Apple Watch replacement for owning and syncing music (rather than streaming it) Is it not possible to sync MP3s to Apple Watches anymore? I have a really really old model, and I selected a few playlists on my iPhone, and when they change, the songs automatically sync to my Apple Watch.