I’m amazed none of these have been mentioned yet. Here are some of my faves
Explaining stuff that’s happening
Real Life Lore (I’m almost signing for Nebula because of him, gorgeous map graphics)
Cold Fusion
Wendover
History stuff
Fall of Civilizations - Hands down the best documentary-like content I know of. Takes forever for new stuff to show up (because research), but it’s so fucking worth it!
Kings and Generals (the narrator butchers every non-anglo name, it really grinds my gears)
Heroes and Legends - The long form, documentary-level videos are amazing. Watch the ones on Gertrude Bell and Voltaire
Gamurrs
Basement Brothers - Almost monotone narration, but possibly the only channel in english that plays and shows several details of old Japan exclusive PC games (PC88 and PC98 mostly)
Russian Badger - There’s a very high chance you’ve seen some of the memes straight out of his videos. Start with “Heavy flamer heresy” if you’ve never seen any.