Chainsaw Man Part 2 (the “Academy Saga” featuring Asa Mitaka) started serialization on July 13, 2022.

It began after a break following the end of Part 1 in December 2020, returning as a digital serialization on Shueisha’s Jump+ platform starting from chapter 98, continuing the original manga rather than being listed as a separate series.

TL;DR: If you’re looking for when Chainsaw Man Part 2 officially started , mark the date: July 13, 2022.

Information gathered from public forums or data available on the internet and portrayed here.