Would you say that there were absolutely no irregularities in the 2020 election?
If you were to say that, that would be a factual statement, that would either be true or false. If it were false, but you believed it was true, that would not be a lie. If false, and you knew it to be false, that would be a lie.
If you would say that there were, or may have been irregularities, but not enough to invalidate the election, that would be opinion. If I said that you were lying for giving an opinion I disagreed with, I would look as foolish as people who keep saying that Trump is lying when he says the election was stolen.