For instance, Wisconsin is a swing state. They had 72% turnout in 2020. Biden had 1,630,866. Trump had 1,610,184. Only a 20k margin. In 2024, there was 77% turnout because of the significance of being a swing state. Trump had 1,697,262. Harris had 1,668,229 -- 38k more votes than Biden in 2020, yet almost 30k less than Trump. Hence, a "swing state" in action.
Now, look at solid blue states. New York had 70% turnout in 2020. Biden won 5.2 million votes. Trump had 3.2 million. In 2024, New York had only 62% turnout. Harris had 4.6 million votes (600k less than Biden 4 years earlier). Trump had 3.5 million. Harris still won the state decisively but had much fewer popular votes than Biden.
Same story in California. 71% turnout in 2020. Biden won 11 million votes. Trump won 6 million votes. Only 60% turnout in 2024. Harris won 9.3 million votes. Trump won 6.1 million. Harris won her home state decisively, but with 1.7 million less votes than Biden.
2020 had strong turnout. It's just math that lead to 81 million votes. Nothing sinister was afoot.