Sound not working on TV mirroring via Airplay or with speakers

There are a couple of components to this:

I have been using Airplay to mirror Zoom sessions from my MacBook to my Apple TV. The picture works perfectly but for some reason I cannot connect to the audio on the TV even though I have selected Apple TV for Audio - I can only hear what comes out of the MacBook speakers.

To fix this I decided to try an external speaker so I connected my Bose speaker via bluetooth (and then via USB) to the MacBook, selected that as the audio output and I had exactly the same result - nothing.

So, I tested this further and I have established:

• No external speakers seem to work when using the Mirror function to Apple TV I tried this with Zoom as well as Youtube
• When I connect my MacBook via bluetooth directly to my Bose speaker without Airplay I can hear sound perfectly when I play Youtube. When I do this for live Zoom sessions, the sound doesn't work so again I have to rely solely on my MacBook internal speakers.
• What is really odd is that I know the speaker works because I can hear it pinging away with email alerts so there is definitely a connection.

HELP! I really am stumped with this. One aspect is that it could be Zoom related, but that doesn't explain why audio doesn't work with other apps in some instances but it does with others.

What can the collective hive mind come up with as a solution??? Thanks!