The mistake in 2016 is most pollsters closed up shop too early because conventional wisdom was the electorate is frozen a month out. IRRC, the few late polls did show Trump closing. Clinton got a huge boost coming out of the 1st debate but lost a lot of ground in the subsequent two, plus Mueller's thumb on the scale late, were all driving movement away from Clinton. The E-MailGate was critical because Clinton had always generated high negatives, there were a lot of people looking for an excuse not to vote for her.
In contrast, Trump's campaign performance by any honest assessment is if anything getting worse by the week, his response to the hurricane has been a huge unforced error, other current news cycle preoccupations like Woodward's book are all working against Trump, and Harris has run a campaign surprising free of mistakes - so far, and Harris' and Walz' public people skills are just better than Clinton's were. Harris has run at far less risk of shooting herself in the foot with off-putting comments in public appearances.