This is just a list of references I used to get a general idea of some of the theories, none of them are in a specific order. For the theories that lack any references, those were written based on what I remember reading from different forums and more a while back.
Genshin Wiki
Old Mondstadt was part of Khaenri'ah Theory
Geo and Anemo Vision Observations
Electro Vision Criteria Analysis
What Symbolism Lies in Character Traits
Visions based on personality
Requirements to receiving a vision
Archon demon names leak
Black Hole Theory
Fake sky theory explained
The meaning behind "the skies in Teyvat are fake"
The abyss sibling is a clone theory