Yes I have seen various polls, but there's a few counterpoints to this.
The election is still around 80 days away, and the first debate hasn't happened yet. I think Trump will win the debates on a personal and policy level, because Biden will be shown to be slow and senile, and the Biden/Harris agenda out of step with the desires of many Americans.
The polls on the national voting average are probably fairly accurate, but the election is not decided by popular vote, but by the Electoral College and state votes. It was the state-by-state polling in 2016 that was wrong in some key states such as Pennsylvania, which is likely to be key again.
Trump can win the election without winning the "popular vote," because as I said above, the popular vote technically does not matter. Hillary won the popular vote by 65.8m vs. 62.9m (a margin of 2.1%), but Trump won 30 of the 50 states and got an EC vote from Maine, compared to 20. It's also worth noting that Hillary's margin of victory in California was 4.3m votes, as well as 1.7m in New York. It's possible that something like this could happen again, where Trump loses the "popular vote" by a couple of points but wins the Electoral College.
(And a side point here, before you claim that it isn't democratic, the Electoral College was designed by the Founders so that politicians would not focus only on the big urban centres and neglect the more rural states. If Republicans win in the rural states, that's because the Democrats don't understand these voters and their issues, or speak to / uphold their values.)
There was said to be a phenomenon of "secret Trump voters" in 2016, who would not answer pollsters honestly or publicly discuss their views, but made their voice heard at the ballot box. There was a Monmouth University poll this year of battleground states this year that claimed 59% of registered voters believe that there are secret Trump voters. Whether or not this is true or will affect the result nationally is unknown, but may swing one or two key states.
Is that enough counterpoints for you?