This claim is unverified because the provided reports describe insider rumors and alleged leaks, while no official Marvel, Disney, or production announcement confirms Tobey Maguire's appearance in Avengers: Doomsday.
Tobey Maguire is slated to appear as Spider-Man in Avengers: Doomsday.

Tobey Maguire reportedly returning as Spider-Man in Avengers: Doomsday and Secret Wars - PRIMETIMER
Source: primetimer.com
Key Evidence
Hollywood Insider coverage in the Hindustan Times reports that Daniel Richtman claimed Maguire would appear, but it also says the character's role remains unclear.
PrimeTimer, Fiction Horizon, Cosmic Book News, the Sunday Guardian, Yahoo Entertainment, Epicstream, and The Direct describe the appearance as reported, rumored, or based on alleged insider information rather than an official confirmation.
Bam Smack Pow directly states that Maguire's inclusion is not officially confirmed, creating a significant distinction between widespread rumor and verified casting.
What the Evidence Shows
The available evidence indicates that Tobey Maguire's return as Spider-Man has been repeatedly reported as a possibility, but not established as fact. Several sources attribute the claim to entertainment insiders, including Daniel Richtman, Alex Perez, MyTimeToShineHello, or to alleged plot leaks. These reports sometimes go further by asserting that Maguire will appear in both Avengers: Doomsday and Avengers: Secret Wars, or that the film may open with his Spider-Man.
However, the sources are not independent confirmations. Most repeat or expand on the same rumor network, and the provided material does not identify an official casting announcement, Marvel statement, studio filing, or publicly verified production record. Bam Smack Pow explicitly characterizes Maguire's involvement as not officially confirmed and frames the available material as fan hope and rumor.
The wording "is slated to appear" presents the casting as settled. Based on the supplied evidence, the more accurate description is that Maguire's appearance has been rumored or reported by entertainment outlets, but remains unconfirmed. The sources also provide no publication dates in the supplied results, so their timing and whether any report has since been superseded cannot be independently assessed from the provided material.