The numbers represent favorability minus unfavorability percentage-point differences. [Sort of net favorability in a sense]. 2016 numbers are based on exit polls, the 2020 numbers are from extremely recent polls.
Biden showing a notable advantage here! Moreover, the numbers suggest that Biden’s favorability may have been recently increasing at least in certain battleground states (insofar as earlier polls this month for the whole nation did not have him doing so well).
What is surprising and somewhat depressing is that Trump has notably gained favorability since 2016. There were no reasons to regard Trump favorably in 2016; there are even fewer reasons now. I truly worry about humanity seeing results like this.