Is Buddhism methodological solipsism? Is Buddhism similar to methodological solipsism, or is it something completely different?
It isn’t solipsistic because the self that can be known is illusory in that it does not have an independent self-nature, and all the qualities that can be known about it are ephemera, i.e., there is nothing that can be identified as an enduring individual.
It is the same for the conscious perception of all ‘external’ things. Even the mind that is taken to be one’s own cannot be so, because neither the self that we constitutionally identify with, nor the contents we assign to our mind, such as thoughts, feelings, and intentions, arise independently from an enduring individual mind.
Breaking through these illusions, which collectively are categorized as being the result of ignorance, is the point of Buddhist practices that lead to a direct experience of the nature (naturing) of mind. Following this path, and accomplishing this goal, does not result in a nihilistic void, because, while the manifestations of mind are not real in themselves, they do arise, and do so in a coherent codependency. And so, the solipsistic agony of a single self locked within itself doesn’t arise (except in philosophical thought experiments, which appear crafted to force a line of thought towards an ‘inevitable’ conclusion, but only by ignoring anything to the contrary 😉).
In its place is found a non-individuated responsive naturing of the whole that we call reality—give or take slight philosophical differences between various extant schools of thought comprising ‘Buddhism’.