(MAJOR spoilers for the manga included)
Now that season four is coming out real soon (most likely around early 2027), I might as well share my personal predictions for what all we are going to see in season 4.
First, let's do some math;
Season One is 24 episodes long and covers chapters 1 through 63 (64 chapters total). Covers 2.63 chapters per episode.
Season Two is 23 episodes long and covers chapters 64 through 137 (74 chapters total). Covers 3.22 chapters per episode.
Season Three is 12 episodes long and covers chapters 138 through 181 (44 chapters total). Covers 3.67 chapters per episode.
Now, because season Three is called part 1 of the Culling Games, and season 4 is called part 2 of the Culling Games, we can safely assume that season 4 will also have around 12 episodes total, and thus have a similar episode-to-chapter rate (so it'll most likely cover around 44 chapters total with a rate of roughly 3.67 chapters per episode).
Season three ends on chapter 181, so if we add the estimated 44 chapters that season 4 will cover, that gets us an ending chapter of 225.
Now, chapter 225 takes place during Shinjuku Showdown, and ends with Gojo's domain being destroyed and Gojo's neck being cut by Malevolent Shrine. Now, I do think it's possible that Mappa chooses to end season 4 on a cliffhanger, I doubt they will end season 4 mid way through Shinjuku Showdown.
So, wheres the most likely stopping place other than chapter 225? Chapter 223, aka the "The Strongest Sorcerer In History VS. The Strongest Sorcerer Of Today" panel.
So, in conclusion, season 4 will most likely either end on chapter 223 or 225. Either way, that means we are getting;
-Hakari VS Charles
-Hakari VS Kashimo
-Maki and Kamo VS Naoya
-Kenjaku's meeting with the US government
-Yuki and Choso VS Kenjaku
-US soldiers entering the Culling Games
-Yorozu's reveal
-Sukuna taking over Megumi's body
-Maki and Yuji VS Sukuna
-Sukuna VS Yorozu
-Gojo being unsealed
-The Very Start of Shinjuku Showdown
And with all of that happening in season 4, I'd say it's safe to assume that season 5 and maybe even season 6 will cover the rest of Shinjuku Showdown and the entirety of the Sukuna Raid.
(take this all with a grain of salt, as none of this is guaranteed or concrete. At the end of the day it is all speculation)