It is not a question of "Did Biden get the votes?" It's a question of "Did anyone get the votes?" If the number of invalid ballots is greater than Biden's margin of victory, there is no way of telling whether he won or not. There is fraud inherent in most of the reasons for an invalid ballot, but that would be on the part of whomever tendered the ballot. If there is also internal fraud, that is a separate matter. The point is that if there were more ballots that should have been disqualified (noise) than the margin of victory (signal), there is no way of telling and the results should not have been certified. Decertification takes the state's electoral votes away from Biden.