Based on the latest Rasmussen polls on the election:

21% of Dems, 43% of Independents and 73% of Republicans supported the Senate's efforts to challenge Biden's election.

We can extrapolate from those numbers.

44 million Democrats X 21% = 9 million 33 million Independents X 43% = 14 million 33 million Republicans X 73% = 24 million

47 million people favored the Senate's effort to challenge Biden's legitimacy.

There are roughly 110 million registered voters in the USA. 42% of them are unsure Biden won fairly.