What are the initial steps to set up the program? about dronebridge

[seeul8er]

The OSD is only an OSD and does not support any touch/menus etc. It should start automatically when the system boots.
What you are missing is a video feed :) Usually, a modified hello_video.bin (the native RPi video player) should start and display the video feed coming from the video_gnd receiving program. Seems like you are not receiving something.
Unfortunatley the Pi4 is de-facto untested since I do not own one and so far no one else took up on the subject.

In your case I would try debugging the entire video pipeline. Check if the raspivid is outputting the stream to the video_air application. Make sure the video_gnd application is receiving and outputting the data via stdout so that the hello_video.bin can read and display the H264 stream.
You could also try receiving the stream on a desktop using the video_gnd. You would need to set the wifi adapter to monitor mode manually.

I am very sorry for the late replies. At the moment I do have other projects and my drone is on hold. DroneBridge is pretty unpolished - some of that because a lot of stuff is not in our hands, like the wifi adapter drivers/firmware etc. This consumes a lot of time during debugging.
I have an idea of replacing the current adapters with more stable hardware, however I do not know when I find time to do it.