Airplay not functioning on macbook pro M1

Having read through the thread created by users trying to use airplay on their new macbook pro M1 to connect to Sony TVs, I can add to this that I'm facing the same problem, but already for simple audio transfer to an airport express, connected to an amplifier. Airplay connections work perfectly fine with my previous macbooks pro, with my iPhone SE, or iPad mini 5, but no way to get it working from my Macbook pro M1 (Big Sur 11.5.1). It definitely looks like an issue of airplay implementation on the mac, since in the sound preference panel, the airport express is listed underneath the full line, separating active sound systems from sound systems one cannot connect to, because for instance in another location. My airport express is at version 7.8.1, which is also the latest one for this device.

Any idea if apple is still working on a fix?