I think jjk is a good series, but it definitely does have pacing problems in different areas to shorten the manga. Here are some arcs I think would help with some of the pacing problems .
An arc before Shibuya where Yuji, Nobara, and Megumi visit Nobara's hometown, maybe as a mission or for her to see her friend, could develop Nobara's character more. This would give more meaning to her flashback before her death and explain how much of the village consists of weirdos.
A flashback arc for Yuki, showing her as the Star Plasma Vessel and her relationship with Tengen, could explain how she developed her ideology and research. This could include a small flashback of her training Todo, reminding us of him before he returns. This would happen when she is talking to Choso and explaining it to him and Tengen before their fight with Kenny. This is needed because, for some reason, every special grade has an arc except her.
An arc with Megumi and Tsumiki, maybe a flashback arc that delves further into their relationship and shows Megumi's love for his sister more.
An arc right after the Shibuya incident that would bring in the three great families and also go more in-depth about the Jujutsu organization as a whole. Maybe after contracting Yuta to assassinate Yuji, they could have also contacted the three great families to ensure the job gets done. Now, past this point, there are two possible routes this could take: either Yuta reaches Yuji first, fake kills him, and the higher-ups find out and send the three great families, or the three great families get to him first, and the arc is about escaping the families until their confrontation with Yuta. The ideal situation is to get more backstory about the three families and the Jujutsu organization while also learning about the impact of the Shibuya incident on Japan. Expanding it to the world might take too many chapters to wrap up, given the amount of time Gege wants to spend on the manga.
The final arc would be the 1-month training timeskip arc. It would start with more depth on what Gojo did immediately after he returned to his students and learned that Nanami and Nobara are gone. Yuji tells him what happened, likely throwing up while recounting the events, which leaves a hard impression on Gojo. Later, alone, Gojo recounts all his failures, with Shibuya being the latest. Despite being labeled the strongest, he feels he has not been able to do anything where it counts, including saving Geto from his path, protecting Riko, and causing the Shibuya incident. He recalls Geto's words: "Are you the strongest because you are Satoru Gojo, or are you Satoru Gojo because you're the strongest?" and "If I were you, would the impossible ideal become possible?" Sick of failing everyone around him, Gojo decides that killing the higher-ups is the least he can do for his students. He kills all of them while also steeling his resolve to face Sukuna and win, not only to save his students but to show that being the strongest can bring meaningful changes, proving it to his students and himself.
After this, Yuji and Gojo visit Nobara, either in a clinical bed or at a grave, to see her condition and determine if she is really dead or not. Yuji talks to Gojo about his experiences, and Gojo gives him advice, trying to be the mentor that Nanami was to Yuji. This not only closes any topics about Nobara but also strengthens Yuji's bond with Gojo, making his death more impactful. We then fast forward to day one of training, where they discuss what everyone will be training and how the last days of training will involve going over strategy. During this, Gojo, Yuji, and Yuta talk to Higuruma and learn about his backstory as a lawyer, the guilt he feels, and how Higuruma reminds Yuji and Gojo of Nanami.
We skip a few days, showing parts of chapter 222 like Yuji training with Kusakabe and talking to Choso about the soul book. There might be a joke about Gojo and Choso meeting, with Gojo asking Choso why he switched sides, and Choso getting adamant about the "brother" talk, which confuses Gojo in a funny way. Around day 15, Gojo is training alone, and Kashimo approaches him. They have a conversation about what it means to be strong, with Kashimo sharing his experiences of dying while being the strongest. Gojo finds it a boring end, and they have a sparring match in which Gojo wins, earning Kashimo's respect. Kashimo wishes Gojo good luck fighting the king of curses.
A few days later, there should be a chapter or two about Yuji's mental state, how Shibuya changed him, and how he is ready to give his life to face Sukuna so the deaths of those who died for him are not in vain. Seeing Yuji's grim expression, Choso talks to him about how even though he has lost many close to him, he still has people who care for him, like Choso. Choso reminds Yuji that Nobara and Nanami didn't just die for him but also entrusted their will to him and would not want to see him die. He tells Yuji to live on for those who trusted the future to him and for Choso, as Yuji is the only family he has left.
A day later, Yuta, Maki, and Hakari discuss their experiences after Shibuya and during the Culling Games. Maki talks about killing her clan and the death of her sister, and Yuta comforts her. Maki asks Yuta if he wants to go on a date after the battle, and Yuta says yes. On the final days, they discuss strategy. During these meetings, the perspective shifts to Sukuna, Kenny, and Uraume. Kenny tells Sukuna about his fight with Yuki and Tengen, and we get a few chapter flashbacks on Sukuna, Kenny, and Uraume's relationship during the Heian era. This is where Sukuna also asks who Yuji is, and Kenny explains how he was created, which is a better placement than during the final fight.
Finally, on the day before the battle, Gojo talks to Shoko about giving Geto's soul some rest tomorrow and admits he is a bit nervous since he is fighting the king of curses. He talks to Shoko some more, telling her to inform Megumi about his father in case he does not make it out of the battle. Then we move to the day of the battle where chapter 223 starts, with Gojo talking a bit more with his students before things play out as they did in the manga.
