followup: someone mentioned on reddit that android:label in the manifest must be filled in now. I already had that, but tried changing it, redeployed, still no listing under 'unknown sources', changed it back to original, did a clean rebuild,redeployed, now LISTED under 'unknown sources'.
Not sure what happened, but that seemed to fix it for me.
Does'nt work. I can reload a previously compile apk and it will re-appear in unknown source. But any newly compile apk does'nt appears even if I can see them in the Headset with a file browser. (note: use unity 2019.2.15f1). Something to do with the new 16 version ???