He says that people were somehow duped into voting a different candidate by unsuspecting voters. You have to read all Trump tweets to speak Trumpese, or read it.
It's now questionable that you could gain anything more by reading his tweets. I've switched to my own name in Twitter, and will post less and less in 2021.
One thing that has happened in years past in some places, and which may very well have happened this year, on both sides of the aisle, is that election volunteers offer to go to nursing homes and help people fill out ballots. Sometimes, the voter is susceptible to suggestion in those cases, and it's not really clear that the final vote represents the genuine desire of the voter. Or that the voter actually knows it is an election year.
It happens. Depending on the laws of the state such things may or may not be legal. I'm sure it is always illegal to tell people how to fill out a ballot, but exactly how much "help" can be offered may vary from state to state.
Another thing I have read about is the charge that poll workers were seen telling people to fill out ballots for Biden. That's illegal. Poll workers are supposed to be completely neutral, and should provide instructions on how to vote, but never in a way that favors one candidate or another. I'm confident that what really happens is something like this.
Voter: (Confused) I don't understand what I'm supposed to do with this?
Worker: Well, if you want to vote a straight party ticket, you fill in the oval at the party preference ballot. That casts a vote for the candidate of all of that parties representatives in all races. Then, you need to choose a candidate for each race in the non-partisan section.
Voter: Huh? What do you mean?
Worker: Well, in some races, the candidates are not listed by party affiliation, so.....
Voter: I just want to get rid of Trump!
Worker: Fill in this oval.
I am also fairly confident that in some cases, a voter expressed approval in some way of Trump, and the tone of voice of the worker indicated some sort of disapproval, and the Republican poll watchers recorded this as bias. In other words, poll workers are human beings, and that offended some Republican sensibilities.