There was a huge ground game in 2020 for mail-in voting. That was not the case this year. It was, in fact, easier to vote in 2020 than this year. Also, Trump finally smartened up and told his base to vote early; something he actively told them not to do in 2020. Was 2020 rigged? Yes. Was 2020 fraudulent to the point of costing Trump the election? No.
They only had to target a few key precincts in the swing states to win. That’s where the cheat happened.