It's important to note that based on the information "Spider-Man: Across the Spider-Verse" provides to the audience about Canon Events, the idea of what is or isn't considered a Canon Event is still quite murky, and it hasn't been completely confirmed that Miguel O'Hara (Oscar Isaac) is revealing the full picture to Miles Morales (Shameik Moore). Nonetheless, "Spider-Man: No Way Home" does address pivotal, canon-defining moments from both the "Spider-Man" and "The Amazing Spider-Man" films — and it smashes through them with a hammer.
In the movie, it's established that Green Goblin (Willem Defoe), Doctor Octopus (Alfred Molina), Electro (Jamie Foxx), and the rest of the baddies that fell into the MCU from the multiverse are fated to die fighting Spider-Man in their respective universes. After all, that's exactly what audiences saw play out in those original movies, and Doctor Strange (Benedict Cumberbatch) is pretty adamant about the importance of not changing that outcome. Nonetheless, by the ending of "No Way Home," Holland's Peter is successfully able to cure the villains and save them from their deaths before sending them back to their home worlds.
"No Way Home" suggests that these villains get a happy ending through Spider-Man's multiverse interference, but there's no denying that their survival disrupts the canon of their original universes in a major way. If their deaths were taken as Canon Events, then per Miguel's explanation, the fabric of their worlds would likely crumble from their survival. Whatever the case, Spider-Man 2099 clearly isn't happy about what MCU Spidey did, seeing how he mentions as much early on in "Across the Spider-Verse."
