If you put your MBTiles file inside a zip and install it as a map package, then it will work. Previously we did support direct use of a .mbtiles file, but moved away from it for a few technical reasons.
You can also configure things like the layer transparency by putting a json file alonside your mbtiles file in the zip. More documentation here: Offline maps | CyberTracker Wiki.
Cheers,
-Justin