Manifest makes TJ's season 2 exit pointless
There were good reasons for TJ's departure in Manifest season 2, but his return in season 4 proved his sudden departure was completely unnecessary.

After The Manifest season 4, part 1, TJ's exit felt pointless. TJ Morrison, played by Garrett Wareing, joins the series in season 2 and travels to Egypt in the penultimate episode. The way he leaves things with Oliver hints that he will be a part of her life, as well as the efforts of the passengers to prevent the date of death. Even so, he didn't make an appearance in season 3, and by making Oliver romantically involved with Levi, his relationship with Oliver is a thing of the past.
Manifest finally had TJ back at the end of season 4, episode 8. Immediately after returning, the character resumes the role of assisting the main character in investigating the summons. TJ joins Olive to help passengers shed new light on Cal's purpose and Omega Sapphire's history. By all indications, TJ should continue to help Olive and the others in Manifest Season 4 Part 2.
TJ Was Supposed To Help The Passengers Resolve The Al-Zuras Mystery

After TJ returned to the series, there was a sense that the character never needed to leave in the first place. It shouldn't be forgotten that when he left, he had a clear goal: TJ Want to do more research on Al-Zuras and his diary and gain new knowledge to help them stop the date of death. Because of this setup, Manifest has to make TJ the key to solving all the mysteries that happened to Al-Zuras and his crew in the 16th century. However, TJ didn't bring back any game-changing information about Al-Zuras' disappearance to justify his long absence from the series. As it stands, the show hasn't properly paid off his exit.
Instead, TJ's only real contribution to the main story after his departure remains the papyrus he sent from offscreen in the Season 3 episode. It ends up helping them a second time in the Manifest season 4 finale, when they use it to decipher a prophecy that Cal might save the lifeboat. That being said, here's something TJ stumbled across in the show's schedule two years ago. It's disappointing that TJ hasn't learned anything else useful since then, especially related to Al-Zuras.
Why Manifest's Al-Zuras Mystery Is So Important

Although the characters have rarely mentioned Al-Zuras since the end of season 2, the fate of the 16th-century Egyptian explorer remains an important part of the story. The myth of the show. The passengers had figured out by this point what the call meant and how all the disappearances were connected, but nothing they learned explained how Al-Zuras and his crew saw Flight 828. Not only that, but they don't know if he managed to survive the date of his death. Revisiting these questions in season 2 could be the step that Passengers needs to take before they can unravel all of Manifest's mysteries.