Now that the TVA no longer prunes timelines, its all canon. In Loki, we saw branches happening all through the timeline, past, present, and future. So anything that could happen, does.
My take on canonicity is anything with a Marvel logo is by definition canon. Movies generally don't reference the TV shows because they don't have time and have to work as self-contained stories. But the TV shows reference the films and each other showing they are connected.
I've been rewatching everything in chronological order this week, and it's not quite as simple as that.
There's what Disney decides is canon and what isn't. The X-Men stuff is part of the Marvel Legacy collection on Disney+, which is not canon to the MCU. The Netflix shows also fall into this category. The Netflix shows are not non-canon for any story line reasons, it's just a business thing. They no longer have a close relationship with Netflix.
Disney can be fickle, though. They used to say the 2008 Incredible Hulk with Ed Norton was not canon, which made sense to me. It tied into nothing else directly, and Norton quit, so I thought of it as a warm up for Iron Man. In What If... they made it clear that Incredible Hulk is canon. When I read up about it, to figure out what to watch after Iron Man 2, I found out that the Incredible Hulk, Thor, and Iron Man 2
all happen in the same week. The Incredible Hulk isn't streaming on Disney+ at all, though, which makes it the only canon thing I've found so far that isn't on Disney+.
Also, last week, I think I saw the Agent Carter one shot listed in the Marvel Legends category. Now it's not there. It's not in the chronological timeline or phase collections on Disney+, either. It's like 10 minutes long, so I rewatched it after Captain America, because why not? It's a fun short. I think it should probably be canon. Why wouldn't it be canon, though? That's a deeper hole.
I think the MCU contains multiple cosmologies. One cosmology has a single watcher, and Kang, and all that stuff. The other cosmology has Agents of Shield, which is a cosmology where there is a race of android watchers, rather than a single watcher, or three watchers like in the comic books, and there is no Kang, and Inhumans are everywhere, doing things that are done by different beings in the MCU film cosmology. Both cosmologies have multiple timelines. The timelines just behave differently, and are run by different people, so they behave independantly. I'll call one cosmology the MCU film cosmology, and the other the shield cosmology. In the shield cosmology, the zodiac vial that Agent Carter took from the thugs plays a big part of the story line, so we can see that it is tied in with Agents of Shield and the Inhumans. Also, after the Agent Carter one shot, the Agent Carter TV show dealt with things like dark energy, which doesn't seem to be a thin in the MCU film cosmology. Cloak and Dagger and Runaways deal with dark energy, too.
So for now, I'm trying to watch the MCU film cosmology in chronological order. I've done:
Captain America
Agent Carter one shot
Captain Marvel (which was way worse than I remembered)
Iron Man
Iron Man 2
I decided the next 2 are going to be:
Incredible Hulk
Thor
Then there's some one shots I haven't figured out yet, and I remember reading somewhere that there's debate about if Thor 2 or Iron Man 3 happens first. It's a fun research project, trying to get it all straight.