You're conflating two separate ideas.
You're combining the idea of cheating at a campaign level and voter fraud/election rigging.
Those are not the same thing.
First, did Trump cheat in the 2016 election? If you consider enlisting or allowing Russian help in his 2016 campaign to be cheating, then yeah. He cheated. (yes, allowing an outside country to interfere with the election is illegal, unethical, and a whole lot of other things). And he did do that.
However, the 2016 election wasn't rigged or stolen or whatever. No one has credibly accused Trump of having the voting rigged or that rampant voter fraud happened in 2016. To my knowledge, only one blogger accused Trump of having rigged the vote, but he wasn't able to bring any sort of evidence that it happened.
Did Trump cheat in 2016? Yes. Did he "rig" the election with voter fraud? No.
But did he cheat in 2020? Yeah. He did. He wasn't stopped. At all. All of that Ukrainian stuff with Biden and the phone call? That was him cheating. All of that Hunter Biden stuff? Very very likely the Russians via the Ukranians. That laptop left at the repair shop? Trump cheating.
Was the election rigged? No. It wasn't.
Both the 2016 and 2020 elections were free and fair. There wasn't any cheating at the voter or vote count level.