Owntone on your local network gives a nice persisten connection to whichever speakers you decided to switch on. The music signal is not being relayed from your phone to the speakers so it doesn't degrade as you move about doing your thing.

You control owntone and tell owntone, enable the speakers in the bedroom, livingroom and deck setting each volume separately and play this m3u playlist of your music, or this album, or this spotify playlist or podcast or whatever to all of them at the same time, synchronized.

Owntone does the job of the apple music/itunes software on a mac (ie the software that ships with a mac laptop to play mp3 files), which does multiroom to airplay 1 speakers. Iphones don't do this and don't do it with spotify. I mean not even an iphone to an appleTV plugged into an amp does spotify reliably. Apple's phone controlling an appleTV box requires constant reboots to function which is enough to stop anybody from using spotify with that setup. Is that intentional? Spotify clearly think so. Doesn't look good but I don't have deeper evidence than these observations of what works and what does not.

Owntone development isn't being controlled by apple for their business interests, eg it does spotify, lastfm and works like apple doesn't in my experience of it with the stuff the devs wanted to work (get involved and hack it to your needs if you have more?) - whatever you think is the reason the apple software not working, it clearly doesn't and owntone does. It works controlled from android, or your laptop, or your desktop, or tablet with the music you want not what apple "allows" or "cares enough to not have be broken" or insert some other excuse (maybe there's a convincing one but I can't think of it).