[sarcasm]Yes, prove that negative. Good luck![/sarcasm]
The burden of proof typically lies with the side that claims shenanigans occurred.
Actually, in the case of elections, the duty lies with the people managing the elections to show they have established procedures and followed them, using documentation and other evidence to PROVE where ballots were cast, who cast them, where they were transported, how/when the ballots arrived at the places they are counted, etc.
Also, the counting process must be monitored, the ballots with errors corrected or rejected, and so on.
In 2020, the evidence shows that there are still questions that have yet to be answered. Mysterious boxes of ballots being scanned after the monitors were told they were done for the night. Stacks of ballots scanned over and over for no stated reasons. No chain of custody receipts for many ballots in many states. Typical 3AM jump in the Dem candidate's numbers after the counting was supposed to have stopped until the next morning. Poll watchers being barred from actually seeing what the workers are doing.
The list goes on. If we can't trust that the people processing the ballots are being held to some strict standard so the chance of "shenanigans" is next to zero, then it's logical and our duty to ask these questions.
In 2020, it seems the people running the elections were not interested in getting the answers.