isRemovableDestination

Accepts only a Storage Access Framework document on a non-primary external volume.

com.android.externalstorage.documents document ids are <volumeId>:<path>, where internal shared storage is always primary. A mounted USB mass-storage volume — which is what a UF2 bootloader drive is — gets its own volume id. Every other provider (Downloads, Drive, MediaStore) is therefore rejected, which is the point: those are exactly where a mis-tap sends the image.