8.3.7 - only AirPlay 2 supported

[Nutul]

I upgraded my old Air from Mojave to Big Sur (11.7.10) and no probs with Youtube, Amazon Music etc to moOde Airplay 2 using the OS system volume to select the Airplay target.

Alas, I can't: I need old apps that don't work on Big Sur.

I think my best option would be to have a 2nd computer with a recent macOs, or a recent iPad.

But maybe it would nevertheless be possible to (re)build the Airplay 1 functionality (although I think that would be beyond my skills).

I still fail to understand what makes your system differently behave from what Tim can achieve - quoting him:

"I have a 10 year old Air running Mojave (10.14.6) and no probs playing to moOde Airplay 2 from iTunes."


which is the same version of MacOS you appear to have. What is it, you use something else than iTunes? Proprietary, non-upgradable software?
Not trying to diminish your needs, just trying to understand... if it's possible for some, it should be possible for all...