There is always a little election fraud. Even in normal times, politicians understand that sometimes overly zealous partisan poll workers find ways to tilt the count.
But only by a little.
My recollection is that Clinton campaign knew of the cases of Republican fraud in 2016. But they did not have enough evidence to overturn the result in a court of law---in five states. So they did not go down that rabbit trail.
I watched several of the "steal" hearings. Most were a sham. But one had credible evidence of Democrat tampering (in Michigan). After the evidence was presented, the judge asked the witnesses to estimate how many votes were tampered.
They said, "Maybe 30 or 40".
That number is not enough to overturn the election.