Who were the "illegal" votes for and how would anyone be able to know?
This has always been the fatal flaw with these audits. For instance, it may be possible to find irregularities but you can never show who a ghost voter voted for.
You may think it's obvious that any questionable votes must have gone for Biden but don't expect everyone else to assume that.
If there are large numbers of fraudulent votes that greatly exceed the margin of victory, you can nullify the results as was done in a recent NC Congressional election where the courts ordered a redo. In the case of a Presidential election, the state legislature can decertify the electors. They don’t have to declare a victor.