Just a note that in the current Alpha verison the external speaker connections don't seem to work.
I've bought a RT-82 external speaker mic adaptor, which I ordered from AliExpress
https://www.aliexpress.com/item/1005005673577923.html
And I just tested it with the official firmware, and it seems to work, albeit with some strange effects, but it does not work with the OpenGD77 firmware yet.
When I plug a normal speaker mic into the adaptor, the official firmware makes some beeps, which indicates it has detected the external speaker mic.
I dissassembled the adaptor and there is a small PCB with various components including a transistor.
I presume that there is a sense input into the STM32 MCU from the connector, but at the moment I don't know whether this is correct or which pin is the input, and I don't know how to switch the audio amplifier output to the external speaker connection