Most obvious is in-person / received late.
Cross check against Maidengate/Out-of-state/felon/no-such-address/double-voted too.
If a majority, plurality, or even significant % of such Biden ballots fall into any of those category, it is dispositive of fraud.
To put the final nail in the coffin :
a) do the same count / analysis in other questionable states b) see if the % holds up under hand recount.
Each state is an election unto itself.