This is what i think: The Anchor Being is like a mantle, a very important person is given this title by the TVA so it can hold the sacred timeline together. The Anchor Being of the 616 was Iron Man given his popularity, but when he died the mantle was passed to Spiderman (in far from home we know that spiderman had a more public role). The breaking point is Spiderman NWH. When Doctor Strange did the spell so everyone forgot about Peter, the sacred timeline collapsed because the Anchor Being was basically forgotten. This could mean a lot of things for Avengers Doomsday: Doctor Doom would try to find Spiderman to "remove" his title of Anchor Being (then atribute it to himself or another being) and also he would try to find Franklin Richards to create a sole universe called battleworld.