If you set an asset folder to a particular encoding setting, all the files in that folder will use that encoding setting.
If you want to set all your files to be built in Vorbis format, there’s an easier way to do that: In the “Build” tab of the “Preferences” window, there’s a list of platforms that your project will be built for. If you click on one of the platforms in this list, you can set a default encoding setting for that platform. This encoding setting will apply to every file in your project, except those files and folders that you’ve specified a different encoding setting for.
Incidentally, if you’ve set an encoding setting for a folder, the files in that folder will use that encoding setting even if the default encoding setting for the platform is different. Similarly, if you set a file to a particular encoding setting, that file will use that encoding setting, even if the folder that file is in and the platform default encoding setting are different.