The Arizona audit DID find that there is no way the vote count should have been certified.

There was no chain of custody for many stacks of ballots, the registry showed intentional logging in and logging out hundreds of times in an effort to reset log data, signature verification for all the votes received an average of 4.2 seconds of time each, dead voters never removed from voter rolls, several thousands of votes were counted for voters also registered in counties outside of Maricopa, several thousand votes counted for voters who were registered as having moved out of state prior to the election, and much more.

The fraud was rampant. But it wasn't "provable" per se, because there was enough plausible deniability for some kind of excuse to be made for nearly everything. However, ultimately, the risk of fraudulent votes being counted was entirely too high to justify the certification of Arizona's electors.