At least with the NYT exit polls, they included phone interviews to account for mail in voters. Here is a more systematic post-election analysis, based on a huge survey (100,000+ respondents), from Fox/Associated Press/U Chicago: https://www.foxnews.com/elections/2020/general-results/voter...

This one shows significantly lower Black vote for Trump than the Essence article (12% of men, 6% of women) but an even higher Latino vote (39% of men, 32% of women). Both sets of data show Trump losing support from white men slightly. (Which is consistent with pre-election polling.)

> This is based on exit polls.

Are there some other measurements based on something else, or is it something we now can never know as a result of mail in ballots having no polling and an expected different statistical distribution?

Exits aren't great in the best circumstances, but early unweighted exits are widely believed to be almost completely useless.

I suggest looking at states like Oregon, Washington, Colorado, Utah, etc. that only do mail in voting and see how they measure what used to be measured by exit polls.

> Are there some other measurements based on something else

For 2016 and 2018, Pew had validated voter datasets, based on people in their American Trends Panel who were matched against voter databases and thus known to have voted. Assuming they do the same thing (or some other reputable firm does something similar, or ideally both) for 2020, that would probably be the best data source.