Solipsism, to quote Wikipedia: is the philosophical idea that only one's mind is sure to exist. As an epistemological position, solipsism holds that knowledge of anything outside one's own mind is unsure; the external world and other minds cannot be known and might not exist outside the mind.
GenAI reduces what once was photo/video/audio proof to uncertainty both through quality (AI can create better fakes) and quantity (it is much easier to use AI to create fakes, therefore much more people will do so).