Well, there was Siddhārtha Gautama, who became Buddha. His original teachings are non-religious.

I can recommend the books of David Hawkins for a modern, scientifically-informed view on the subjective experience of Reality.

https://veritaspub.com/dr-hawkins/

> Sir David R. Hawkins, M.D., Ph.D. was a nationally renowned psychiatrist, physician, researcher, spiritual teacher and lecturer. The uniqueness of his contribution to humanity comes from the advanced state of spiritual awareness known as ” Enlightenment,” “Self–Realization,” and “Unio Mystica.” Rarely, if ever, has this spiritual state occurred in the life of an accomplished scientist and physician. Therefore, Dr. Hawkins was uniquely qualified to present a spiritual path that is scientifically compelling to modern society.

There are a few of us out there trying to do exactly that, including the above article.

It has already been done. One of the oldest Schools of Indian Philosophy called Samkhya (which is atheistic) has a very beautiful model of the Universe/Elements/Evolution of the World which has influenced all other Schools (including Buddhism) and is worth studying.

You might find the book Modern Samkhya: Ancient Spirituality for the Contemporary Atheist a good starting point.