Yes, there is functionality to create groups in music assistant. You can even create groups between different types of sinks (so you can combine say Chromecasts together with home assistants media player together with airplay). However, I have not played around with that too much so I don’t know how well the players will sync with each other.

Given the lawsuits against Google from Sonos in the last 5 years, it doesn't seem to be low hanging fruit. Might not exist yet.