Partial Solution : Side load mmpk into active logged in Account Folder.
I've recently found that mmpk's will function properly if put in a user (or guest) folder within field maps.
e.g. PC\Nokia 6.1\Internal shared storage\Android\data\com.esri.fieldmaps\files
We just can't put it in the mmpk folder that is supposed to allow anyone to use it. This is not a cure-all, but another option. Of course you will need to put the mmpk within the mmpk folder within the user (or guest) folder. On my phone it works in all three of the blue circled account folders. My phone is not setup for sd card storage, so I have not tested this location out yet.
again, the above circled guest account could be substituted with any account folder.
Hope this helps. It still is not there.