This claim is very interesting and struck my curiosity as I had no idea this was a claim. After doing some research and looking through some articles I found an article by USA today that talk about how "Conspiracy theorists who, months after the 2020 election, still falsely claim voter fraud affected the outcome have started to get creative." And that there were people who claimed that Biden had gotten an excess of more than 8 million votes on top of the legitimate ones that he had gotten. An alleged election expert Seth Keshel claimed that trump had previously won multiple states including "PA, MI, WI, NV, AZ, GA and MN," another article I have found on my search to see whether this is a valid claim or not was Yahoo News which informed me that the Trump administration had hired 28 different international experts who had reported to the administration that they found zero evidence of fraud. It also said that New York Times had spoken to 49 out of the 50 election officials and all of them said "Not one, Democrat or Republican, reported “that fraud or other irregularities played a role in the outcome of the presidential race.”" which on top of all the other reasons for which the election would not be a fraud there were multiple professionals and government officials from both parties stating they saw no fraud in the election.
The 2020 election wasn't 'stolen.' Here are all the facts that prove it.
Fact check: 8 million 'excess' Biden votes weren't counted in 2020