Warning: Contains Venom: Let There Be Carnage.
The post-credits scene in Tom Holland’s Spider-Man.
Previously, it was believed that the Venom films took place in a different canon than the MCU. The Spider-Man movie rights are complicated and can be a bit confusing, but the gist is that Sony still holds the rights to the character and allows him to feature in the MCU through separate deal with Marvel. Sony is currently in the process of setting up its own cinematic universe of Spider-Man characters, which will include Kraven the Hunter, and the Venom films. Now, it looks like Holland’s Spider-Man could be a part of that universe as well.
So, how do Eddie and Venom get from reality to the MCU? Spider-Man: No Way Home. It's a fair guess seeing as how their jump to the MCU was accompanied by a singular blinding flash of light, which is the same thing that happened in the No Way Home trailer at the moment Strange cast the spell and it went awry. Another possibility is that Venom’s accessing of the symbiote hivemind through Eddie caused something to malfunction in some way. Considering how hard the characters of MCU's Phase 4 have been tampering with the multiverse, it's even possible that it was an entirely different multiverse event that brought Eddie and Venom to the MCU.
Since other major characters from past Sony Spider-Man films like Alfred Molina’s Doctor Octopus and Jamie Foxx’s Electro are returning in No Way Home, it wouldn’t be out of place for Hardy’s Venom to show up as well. There’s been no confirmation yet that he’ll be in the Spider-Man movie, but because both franchises are produced by Sony Pictures, it seems most likely that Eddie’s arrival in the MCU is tied to the multiversal chaos in No Way Home.
Of course, there are still a number of things that haven’t been revealed about the MCU multiverse, any one of which could be to blame for Venom’s sudden change of reality. A powerful Scarlet Witch was messing with the Darkhold in Venom: Let There Be Carnage sets up a lot of exciting possibilities for the character’s future.
