I actually did my degree thesis on designing electronic voting systems (and built one), and ultimately concluded it was impossible to make them fully secure. The best you can do is paper backups and random audits to detect anything illicit followed by a full audit if that fails. No paper backups results in it being undetectable.
Computers are good at making things more efficient, but in terms of election security the inefficiency is a feature (i.e. it takes more people to alter votes, and the more people you add the harder a lie is to keep).
[0] https://thehill.com/policy/cybersecurity/457168-report-says-...