This question is based on my assumptions/understandings of the following:
- Way back in the past, there was a multiversal war.
- “He Who Remains” fought his variants and won the war.
- “He Who Remains” united all timelines into one main one before the events of any shows we watched.
- What we watched as the MCU shows happened while “He Who Remains” was taking care that no branching happened.
- At some point, “He Who Remains” dies, and branching starts to happen.
We know that up to the point of Loki stealing the Tesseract and being taken by the TVA, there was no branching in the main timeline. Some time after that, “He Who Remains” dies, and branching starts.
Also in Loki, we learned that the TVA allowed the Avengers to time travel as it was meant to be (Avengers: Endgame). So we should be sure that no branching happened, at least not to the point of Thanos' defeat in Endgame.
Do we know, or is it possible to know, at what point in the MCU does the branching start?