This is why crypto hardware wallets have screens.

To show you the user something and no one else without leaving a paper trail.

The ability to enter a single person voting booth through a e-passport style gate and security to check your devices screen again so a perk that could be implemented.

The public ledger of all votes that could be checked to enforce no duplicate voting, generate a full list of who voted if desirable, and you with your device in a secure room check your vote.

Are all features of cryptocurrency systems that exist allow.

All of that could be optionally allowed or disallowed for a future cryptography enabled voting system.

The e-passport style gate to single person voting room is the physical security needed to ensure people don't coerce each other more than today. And optionally make coercion impossible at the cost of some people not being able to vote (people who need someone in the room with them as they do in the booth with them today).