Store variable in all the Scenes

i have a simple ui, and i register the value in the scene like this:

bpy.types.Scene.render_folder = bpy.props.StringProperty

but if I move to other scene its lost the data from the last scene and any scene have its own data in that var,
how can I store (or register) the variables in the “blend” file or in a global space so I can get it from all the scenes?

To my knowledge there is no way to register an app level global variable short of storing it in add-on prefs. It’s easy enough to write to a file, so that is always an option as well.