It’s all explained in this overview:
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Regardless of the Android version, all media files in external storage can be read.
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However, write access is only available for certain Shared folders (
/Documents, /Download, /Music, etc.). -
For non-media files, write access is only available for these two Shared folders (
/Documentsand/Download). -
However, full access (read / write) to the ASD and the private directory (internal storage) only exists for the respective app.
Note: Read / write access to the Shared folder should not require
READ/WRITEpermissions on Android 11+ (neither for media files nor for non-media files). This bug with Niotron & AI2 has not yet been fixed, although I have pointed it out several times.