In the Season 1 of Marvel Studios' Loki, Sylvie, an alternate timeline Variant of the titular trickster Asgardian, stabbed dead the individual known as He Who Remains. Jonathon Majors' Kang Variant's continued existence was the only thing preventing the MCU's timeline from fracturing every which way. This Multiversal turmoil was further exacerbated by the events of the MCU feature films, Spider-Man: No Way Home and Doctor Strange in the Multiverse of Madness.
Loki, as a series, was primarily focused on alternate timelines where one single thing was changed. No Way Home, Multiverse of Madness, and Marvel's animated series What If...? centered more around alternate realities where a vast amount of things are different from the main MCU.
As seen in the Doctor Strange sequel, there are alternate realities where the laws of physics don't even apply, hence the universe where everything is made of paint. For those who aren't paying incredibly close attention to the ongoing MCU, it might be easy to become disoriented while trying to make sense of all the rules and intricacies of the MCU Multiverse, but a Marvel Studios producer is helping to set things straight.
Are Marvel Timelines and Universes the Same?
“At that moment, the Multiverse expanded indefinitely forward into the future, back into the past, sideways, left and right, to alternate realities we can’t even comprehend. If it wasn’t for Sylvie, we wouldn’t be here right now.”
The producer continued on the distinction between alternate timelines and alternate universes:
“There’s a slight difference between alternate timelines and alternate realities, but they do intersect, and they end up being one and the same. Our characters wouldn’t have been able to interact with them, definitely not in the way that they did in Spider-Man: No Way Home and Doctor Strange in the Multiverse of Madness.”
"Who Are You in this Vast Multiverse?"
The MCU Multiverse will no doubt continue to expand. It's interesting that Palmer said timelines and realities can intersect and can become one and the same.
In Loki, a timeline was only able to be safely eliminated before it hit what the TVA called "the red line." Once a timeline lasted long enough to reach that line, it had the potential to become a full-blown alternate reality. And with Sylvie murdering He Who Remains, the whole Multiverse is vulnerable to his Variants, some of whom are quite evil and bent on total dominion over time and space.
For the viewers of the MCU however, the Multiverse has proven to be a lot of fun. After all, it brought the two former cinematic Spider-Men, Tobey Maguire and Andrew Garfield, into the mainline MCU to team up with Tom Holland's web-slinger for a high-stakes adventure in No Way Home. This likely would not have been possible had Marvel Studios not decided to pursue this Multiverse-themed story arc.