>>82062553We have no way of knowing how much of our sensory experience is generated entirely internally without external stimulus of any kind because total sensory deprivation from birth is impossible and even if it were possible, results in a total inability to communicate any meaningful information about internal experiences.
There has to be positive evidence that our surroundings are real, and to do find that evidence we have to account for all wholly internal experiences. Any particular perceptual "point" of our surroundings could be collectively hallucinated.