I have experienced a state often called the "clear white light of reality" or "unity consciousness" during a long (6+ hours) meditation session. It's a state written about in the Tibetan Book of the Dead and Tim Leary's The Psychedelic Experience, and tons of other books. My bet is lots of people have been there tbh, it's really unmistakable when it's happening to you.

BUT, I don't think that's necessarily the "non-dual" state. Maybe it's one of the non-dual states, but if non-duality is real than it can be "accessed" anywhere, anytime. You often hear that encapsulated in the "gateless gate" idea. A teacher I like says that it's not when we go to the white light, it's when the white light comes here.