Reply from JC on Twitter:
“You need the WRITE_EXTERNAL_STORAGE permission in your manifest, then you
can write to /sdcard, which is what is visible when the HMD is plugged
into a computer. Implementing some kind of cloud transfer would be more
convenient for users.”
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
and set android:requestLegacyExternalStorage="true" in the <application> tag
in Unity:
string fname = System.DateTime.Now.ToString("HH-mm-ss") + ".csv";
string path = Path.Combine(Application.persistentDataPath, fname);
file = new StreamWriter(path);