Pixhawk 2.4.8 IMHO has no built-in OSD chip (and neither camera input for nor VTX output for analog equipment). Therefore there are probably no OSD settings.
For using digital HD video this is a very unfortunate solution, because now a custom build is always needed for the OSD to be adjustable.
DJI Ocusync is already a little older and hardly in use. Forget it better …
Current is today DJI FPV with WTFOS, HDZero or Walksnail. All of them can be fed with OSD data by Ardupilot … if the OSD feature is integrated in the Ardupilot firmware. For FCs without OSD chip this is IMHO not the case.
You are taking the conversation in a completely different direction.
The topic of this post is why OSD parameters are not appearing under Plan 4.3.1. That’s it. if you don’t know the answer its ok. the developer will jump in. @tridge is the gate keeper of Arduplane code.