Noticed it wasn’t answered in my other Beyonder related question. Does the Beyonder know about the Beyonder race? If not, why?
Initially, The Beyonder actually did not know anything at all as he was a Cosmic Cube simply existing as an entire universe. He was "a creation complete unto himself." He literally was an entire reality. All knowledge about anything other than himself was simply incomprehensible to him - the existence of other beings was a surprise. When Molecule Man's experiment punched a hole into our reality he saw something more than his reality for the first time. The beyonder's vast power exceeds anything before or since except that he is constrained to a set timeline, and he is extremely naive. Although he describes himself as all-knowing and omniscient, he literally has to learn absolutely everything through direct experience.
In the end, however, the Rachel Summers Phoenix was able to overtake him by revealing all life in the cosmos to him - the essence of what Phoenix is. In that moment, by definition, he had to know about the race of Beyonders because the Phoenix made him experience every life in the cosmos at that time. After that moment he was aware of every race, every species, and every living thing. It crushed him.