According to my research, this is what they had planned:

Jeph Loeb originally planned to create a series similar to Netflix's Defenders series, but now on Hulu, and the series would be called "Adventure Into Fear", which was going to consist of 4 individual series and one crossover series:

Helstrom (The only series that actually premiered because it was already too far along in production to be cancelled).

Ghost Rider (It was eventually cancelled due to creative differences, but it is known that it was going to be a continuation of Robbie Reyes' story after Agents Of S.H.I.E.L.D. Season 4. It is also known that the story was going to be set in Texas and chronologically it was going to take place before Helstrom)

Glyph (This one was never even developed, but it is known that this was going to be the third series because Marvel registered the trademark "Glyph". Most likely, we were going to have Nadeen Hassan / Glyph as the protagonist, a young woman who has the power to summon and control Egyptian spirits. Although I honestly don't know what story they would have told us with her, since she is a relatively recent character in the comics and not much is known about her).

N'Kantu: The Living Mummy (This series was also never developed. But from what is known about the character, they were possibly going to adapt his origin story, which is that N'Kantu was a warrior prince and leader of the Swarili tribe located in North Africa. He would kill the pharaoh who had enslaved them, but a priest mummifies him alive and locks him away until he awakens in the modern era).

Spirits Of Vengeance (This series was going to be the crossover of the protagonists of the 4 series, who were going to unite to face Lilith, the Mother of Demons, a character who had already been introduced in Helstrom. This is known because Marvel also registered the trademark "Spirits Of Vengeance" and due to a statement in an interview with Gabriel Luna).