There’s no indication over the last month in the non-live interview polls that Trump supporters last month are merely saying that they are “undecided” right now.
Nor is there any reason to think that the surveys are shifting because Democrats are more likely to answer polls these days. Many of these non-live interview pollsters weight by party identification, so they’re less susceptible to fewer Republicans responding than have over the long term (like when the race for president was closer).
I also checked out the state polling done since the protests began. Averaging the non-live interview polls just like I did for the national polls, I found on average that Biden’s margin was 9 points bigger than Hillary Clinton’s was. A 9-point shift in Biden’s direction nationally from 2016 would give him an 11-point lead nationally, which is around where the national polls have the race.