The Arduino code is for converting for the new DJI FPV ODD system specifically. The Ocusync Air system has native basic Mavlink Support.
The original Ocusync system does not have anywhere near the same level of OSD available and the Arduino will likely not work on it as it’s a different OSD comms
The New FPV system supports basic MSP osd and the new “custom” Betaflight OSD thst gives you all of the additional info.
You won’t get anymore on the old Ocusync System than what it shown as basic as it’s simply not got it.
I have been working on a video on this and it will go out this week showing how to setup.