What is the most high leveled Maths and Science theory?
I love your question. High leveled is a bit of a loaded phrase. It hints at what I believe is a major misconception about mathematics. That is the belief that what is profound in math can only be understood by a few people.
In my opinion, this couldn't be more false. There is, of course, work to be done in climbing the mountain. But the aim of mathematics as a whole, is to make that climb as easy as possible; the goal is simplicity. Simpler proofs are always favored over complex ones. Anything that can't be understood by the majority of mathematicians is generally regarded as poorly constructed.
I'll let you in on a secret. Most mathematicians and physicists are not considerably smarter than average. They don't have superhuman intellectual abilities. They have just spent a lot of time studying and love what they do.
It reminds me of a story that is commonly attributed to the physicist Arthur Eddington. Asked in 1919 whether it was true that only three people in the world understood the theory of general relativity, he allegedly replied: 'Who's the third?"
Of course, this sounds a bit funny to a modern physicist because today, every serious physicist understands general relativity. Is that because modern physicists are smarter, or somehow better? Of course not. The lesson to be learned here is that there are only two types of theories in mathematics and science that are only understood by a small number of people: those which are new, and those which aren't very useful.
To answer your question, there isn't really anything that I would describe as a "high level" theory (in the way you define it) in math or science. Once you get past a general education, there are active areas of research with relatively small groups of experts (not because the material can't be understood by most people, but because researchers usually specialize in one area due to time constraints). You can learn more by reading journals in the areas of research that interest you.
What you should be asking is, "What is the most profound branch of mathematics or science?"