So if i just create a /transcode folder in my shared folder it should work?
Provided the container points to that, however, I should read this and this to ensure that it will work, I'm not a Plex user but I have watched some of the videos, so I understood what you meant by AppData.
Raid is not a backup! Would you go skydiving without a parachute?
He skips the part with the transcode folder, and in the comment he says: "Just make a transcode folder in your AppData folder. You will be very happy!"
How do i find the AppData folder
You can create the transcode folder anywhere you want, you can name it anything you want, and it does not have to be an OMV shared folder. The only requirement for it is that it has the correct ownership and permissions such that the Plex docker container can read and write to it, and you correctly specify the linkage between the Host Path and the Container Path /transcode in the container setup.