"Why do we (humanity) exist?" "Because our species evolved to this state."

"Yes, but why are we capable of asking why do we exist?" "Because our species evolved the intelligence necessary to understand our existence."

"Yes, but why did our species evolve with the intelligence we have?" "Because it was an adaption to our environment that made our offspring more likely to survive."

"Yes, but existentially, why does all this exist to the point where we evolved to that state?" "Life evolved on Earth, we don't know how that process began. We have some theories, but nothing proven."

"That's not good enough!" "Sorry, that's all we've got so far."

https://www.britannica.com/topic/first-cause

I believe this philosophy go even further back into the various Vedas of ancient times too, which also discussed multi-dimensionality and everything consisting of frequencies / vibration. The Gods are really encoded symbols and personifications for various aspects of Cosmos (creation, maintenance, destruction, etc).

Some people seek into the mystical. Other people seek into science. Some people don't seek, and for them there's less logic. Logic though, can also be something that binds you to falsehoods. Revisiting first principles again and again is healthy, but really tough work.

Science and meditation should go hand in hand. Being brilliant is no safeguard against personal angst and delusions.

We don't know yet, is the perfectly fine answer. It's OK to seek too, which is how people find new solutions.