You’re right, but the AirPlay protocol has been updated over the last 9 years. I found something called UxPlay and it works pretty well. https://github.com/FDH2/UxPlay

I think its really great. Im using the server component together with spotifyd and then have the clients running on a few different devices. The sync is really good and you can adjust the delay of each device in the web interface. I mostly needed that because of a bluetooth speaker and a sound receiver which delays always by 250ms no matter the input. But now i have music blasting from every room and you can ealk from room to room and dont hear any delay. You can even have different soundsystems in the same room and it is not even noticable that there are different devices playing. I totally recommend it for a music multiroom setup. On my main pc i’ve even added it as an audio output device with pipewire :)