Then again when I look at the list of supportet phones it's not so great either, while a lot of iPhones is listed the support for i.e. Samsung is only for devices which are a couple of years old. I.e. it works like a charm with my Samsung S22 Ultra, so no problems here.

So this begs the question if there is an issue with different / non supporting protocols / profiles?

It's not perfectly clear to me if protocol and profile are the same thing, or not?

From the documentattions:

DJI Mic2 transmitter supports bluetooth protocol BR / EDR (basic rate / enhanced data rate).

GoPro Hero12 supports HFP / HSP profile ( Hands Free Profile, Headset Profile).

That said the documentation for the Hero12 clearly shows that the BT audio is targeted at headsets: https://community.gopro.com/s/article/HERO12-Black-Bluetooth-Headset-Support?language=en_US

Documentation for DJI Mic2 and mobile phone compatibility list: https://dl.djicdn.com/downloads/DJI_Mic_2/compatibility%20list/DJI%20Mic%202-%20Mobile%20Phone%20Compatibility%20List_EN.pdf

And; while the DJI Mic2 works with their own products like Pocket 3 and Action 4, it also seem to be supported by the latest Insta360 AcePro action cam. So clearly not a DJI exclusive support either.

So finally my question; is it probable that the GoPro BT audio is implemented in a way which will not be compatible with the latest DJI Mic2 transmitter?