this is a set of shoes containing zero pairs of shoes = { }
the fact that there are no shoes no shoes in it doesn't change what it is.
Ok. A multiverse composed of zero universes is a multiverse.
A pair of shoes composed of zero shoes is still a pair of shoes.
I'm an only child but I'm still part of a pair of twins. Alright. Let's suppose.
There's a multiverse composed of one single universe during the entirety of He Who Remains' administration of the TVA after he unified the timelines, making the events that happened during No Way Home and the sequel to Dr Strange impossible. Sylvie's actions led to the creation of an infinity of other universes that filled up this conceptual, non-effective multiverse, making it a reality that justified plots based on the multiverse.
For simplicity, since this perspective doesn't seem to affect my understanding of the Loki series or phase 4, I'll refer to every multiverse composed of one single universe as a universe, every pair composed of a unique individual as an individual, and every only child as just an only child, and not a half of twins, a third of triplets, a fourth of quadruplets, etc