AnkiDroid doesn't detect apkg file in the requested location
Strange, it should be seen in the Import dialog. Please fill a bug report at https://github.com/ankidroid/Anki-Android/issues thanks!

Meanwhile, you can use the second method for importing a .apk file:
https://ankidroid.org/docs/manual.html#_open_the_file_using_android
Just install any file explorer (like File Manager), and tap your .apkg file. It will open in AnkiDroid.