Is it possible to prove (or disprove) election fraud without access to the ballots?

Ballots are guarded more closely than transcripts of Presidential phone talks with foreign leaders. So how can anybody say that there is or is not evidence of election fraud?

In many states, taking a selfie of your completed ballot and sharing it on social media is a crime. See
https://www.ncsl.org/research/elections-and-campaigns/secrecy-of-the-ballot-and-ballot-selfies.aspx

Many other states modified existing laws to permit voluntary disclosure of how an individual voted. However, the actual ballot in the possession of the election officials is guarded from everybody.

If there is any fraud in elections, it cannot be proved or disproved without an analysis of actual ballots. For instance, if you suspect a forged signature, how can you prove or disprove it without a comparison of the two signatures?

Therefore, can we just disregard all statements about whether there is or is not any election fraud?