OK. I usually reply on Real Clear Politics because it averages the top polls and shows you their work. I have found them right on the money for Senate and Congressional races, and state races.
However, in 2016 ALL the polls were way off (if I am not mistaken). Either undersampling Rs? over sampling Ds? Trumpsters disguising their preferences? corrupt media? Who knows why. The same could be and probably is afoot in 2020, or maybe not.
Here is current showing (with Trump down across the board):
https://www.realclearpolitics.com/epolls/2020/president/us/general_election_trump_vs_biden-6247.html
With four months to go, lots of events/issues will impact the polls along with the fact that most voters don't look at the candidates until after Labor Day. Debates (3), conventions, the virus, the economy, China, Ukraine, Durham indictments, October surprises, etc. all in the mix.