They’re both cultural stories that were probably based on several actual historical figures at some point that were combined and mythologized over centuries.

Take Arthur. You could maybe find the origin of the character in some Celtic leader fighting the Romans, then as people retell stories he gets merged with a different guy, and then when the Anglo-Saxons invade new stories get added and repurposed etc etc and now the French hear about it and decide it needs a love triangle where the English king gets cucked by a French Chad Knight, boom, now you’ve got a medieval courtly love story from someone once talking about the time Athor’lescs’op once stole some Roman sheep.

The Yellow Emperor is the same thing. There probably was a Chinese warlord who paid for some irrigation ditches and wasn’t too big of an asshole to the peasants, and another one later who built some libraries, so they’re “based on a historical figure” but mostly the stories are just cultural myths that make good entertainment and maybe work as a morality play.