The fact that they teased Spider-Man: No Way Home in the post-credits pretty much solidifies this Venom in the MCU. Why else do it? Unless this was a drop-the-mic end to Hardy's Venom and a passing of the torch to Disney to do their own thing which doesn't make any sense either. My only hope is that it was tease as is common in the Deadpool films, where they just nod to the MCU and go about their merry way, but that post-credit scene was too on the nose to be so readily dismissed.
What really jumps out at me is that in the teaser it's just some clip of spider-man on TV, it was clear this was not a collaborative effort between Marvel and Sony. It screams no one got Tom holland out of bed and had him go film a scene for Venom. I'm not privy to the details, but I believe theres a licensing colab between Sony and Marvel. Marvel films spider-man, sony contributes to the budget and advertising and they get a cut of the proceeds, but Disney has complete creative control.
With Venom thats a Sony specific property and Marvel wants nothing to do with it
1. Because they cant maintain creative control
2. It doesn't really make them any money.
3. Because it makes Sony money which in turn make it more difficult longterm for Disney to buy the IP back.
Now the big caveat is Multiverse. Could venom make a non-impacting cameo no way home? *shrug* maybe, idk. I suspect not. Disney don't want no scrubs. With Raimi going to Marvel and the Fan nostalgia for the spider-man movies version of Doc Ock and Green Goblin I can see Disney saying something like "ok you can teaser Spider-man as part as our deal to let us use Doc Ock and Green Goblin for a Cameo", but this version of Venom doesn't exactly have rabid fans ready to give Disney money. This is my personal opinion, but I just don't see it.