One small problem - the voters’ signatures and identifying information are on the envelope which contained the ballot, and the envelope is discarded after the envelope is received, validated, and processed; this ensures the information on the actual ballot slip (how the voter voted) remains secret (as required by law).
There is no actual way to match up the ballots (which have no voter identification on them) with the envelopes, even if they had kept the envelopes. This is why they can do a recount (how many votes did each candidate get), but not who voted for which candidate (because this would be illegal, as it would defeat the whole "secret ballot" thing).
https://ballotpedia.org/Processing,_..._Georgia,_2020
You would have thought that the President (or his lawyers) would know this...