Over 30 million people have voted so far! That's 21.7% of the total who voted in 2016 (about 138 million). This year, it is expected that 150 million or more might vote, so it's probably about 20% in the bank.
Democrats are doing a great job of getting out and voting early. Obviously, the most committed people will vote first and we have a long way to go, but we have a lot of votes in the bank and a lot more than Republicans.
I think the Republicans are making a big mistake by bashing mail-in voting and they don't seem to be encouraging early in-person voting either. There is nothing wrong with voting in person on election day, but getting votes in early helps to avoid unexpected events - bad weather, virus outbreaks, your car not starting, etc. On the campaign level, it also allows the Biden campaign to see where votes have been cast and where they are outstanding. The Republicans have a lot less early votes in so they are more in the dark.
Here is the cool early vote tracker I am keeping an eye on:
https://electproject.github.io/Early...20G/index.html