Hand counts were done by two people teams, a republican and a democrat who had to agree on each ballot. They did so under the watch of partisan observers. Any ballots in dispute went to the election commission for a three person panel to review.
They didn't use the dominion barcodes, but instead the readable text that the voter who cast the ballot verified was in accordance with his vote, before submitting it for tabulation.
In essence, every ballot for Biden had Bidens name under President, and every ballot for Trump had Trumps name under President.
Their ballot actually had the name of the person they voted for printed on it so there could be no fraud.