I still do not get it.
Do you expect people to have files created by your app reside in a user folder and users to navigate there with the os and open the files?
Or do you expect people to open the app and then use the app to open different files.
Because file extensions on system level only matter for scenario 1. Or is this fundamentally different on mac? When I open , for example, a picture viewer and select open file, it prefilters the folder I am looking at, with pictures. But for a picture viewer, it is handy to use the os file browser and just randomly open a file, without opening the app first.