If you pull up "Presidential General Election Turnout 2012-2016 County and Municipality.xlsx" what you find is that Wisconsin uses estimated voting age population (rather than registered voters) for its turnout denominator. In 2012, there were 3,080,628 votes out of 4,378,741 estimated age appropriate voters, for a 70.35% turnout. 2016 dropped to around 2,965,685 votes, with a higher 4,463,565 estimated age population, for 66.44% turnout.
The "Voter Turnout Partisan-NonPartisan Through August 2020.xlsx" suggests that there are now 4,536,417 estimated age population voters. … Published reports show 1,630,542 votes for Biden, 1,610,007 for Trump, and third party candidates having 38,414, 5,253 and 5,205. That's a total of 3,289,421. That voter turnout, using the same benchmarks, would be 72.5%.