I'm confused. The tweet doesn't say that a_n is monotone nom-increasing, but the theorem isn't true for non monotonic a_n.
D_0 = 10, D_1 = 10, D_2 = 1
a_0 = 0, a_1 = 9 ≤ 10/(1+1) is false
https://twitter.com/damekdavis/status/1730983634570510819/ph...
Tao's proof assumes a_n is monotonic non-increasing.
Did the OP tweet just make a mistake that Tao ignored?