That’s what statistical audits of the paper ballots are there for.
Secrecy of the ballot is an official Good Idea. All kinds of possible abuses become possible in systems where you can figure out who voted for whom.
Votes on legislation in Congress are not at all comparable.
Although it would be interesting, as an intellectual exercise at least, to consider how secrecy there might work out, too. Recalling the old Molly Ivins definition of an “honest Texas politician” as one who stays bought…