Worth a shot I guess. I also confirmed I'm using a go2rtc stream in my home assistant card with MSE as the go2rtc mode. Not sure if this is going to work but I'm attempting to attach a screenshot of my card settings in case there is anything there that may help

(edit) - Can't quite figure out how to get a pic to display...

I'm no expert but I'm pretty sure I had to add the output_args record: preset-record-generic-audio-aac to get audio on one of my cameras. Maybe give that a try?

##### Cams #####
cameras:
  front_door:
    ffmpeg:
      inputs:
        - path: rtsp://redacted/h264/ch01/main/av_stream
          #input_args: preset-rtsp-restream
          roles:
            - record
            - detect
      output_args:
        record: preset-record-generic-audio-aac
    objects:
      track:
        - person

Mealie has been solid for me