Try this
Move your savefiles to <Internal Storage>/Android/data/com.ProjectPokemon.PKHeX/ (I used the app "Files by Google")
Now open your savefiles from <Internal Storage>/Android/data/com.ProjectPokemon.PKHeX/, you might now be able to save changes without changing anything from the app
ctto: ChristopherHX
This works for me. I'm using an Android 10 phone.