Not really. Whilst paper voting fraud is definitely possible - maybe even easier than online fraud - in an election, paper ballots are distributed across an entire country. They require "hacking" 1000's of people in order to corrupt a national vote. Computer hacking just requires breaking the security of one application.
I find it hard to believe that a modern identity infrastructure (which we don't have, admittedly) combined with basic cryptography can't get us where we need to be.
We might not be able to cryptographically prove anonymity, but all it takes is trusting the government to anonymize the data correctly and make it secure in transport.
> trusting the government to anonymize the data correctly and make it secure in transport
Large banks don't always succeed at that. The government makes huge mistakes all the time. What makes you think this is possible?
The issue is that perfect security is impossible either with physical or digital voting. All we can do is minimize the consequences of an inevitable mistake or breach.
You can still hack open source though. Some of the highest profile security projects like openssl get hacked. Sometimes it just takes a simple misconfiguration to get hacked, like with Debian a few years ago.
The point is, computers provide a single point of failure. Bribing enough of a country's electoral officials to shift a vote without being detected is immensely more difficult in comparison to finding a zero-day in some voting software.
The only guarantee that open source provides, is that we'll probably find the bug eventually. A malicious state actor that wants to influence an election has absolutely no incentive to let people know that they've found a vulnerability with any sense of alacrity.
Most arguments given against online voting systems are equally valid arguments against in-person voting and especially against mail-in ballots.
Those arguments are the red herrings.