A few that I am not sure if I have seen mentioned yet.

Jackson Crawford, Old Norse linguist.

https://www.youtube.com/channel/UCXCxNFxw6iq-Mh4uIjYvufg

Drachinifel, deals with Nautical history and ship design.

https://www.youtube.com/channel/UC4mftUX7apmV1vsVXZh7RTw

Greg's Aeroplanes and Automobiles, I don;t really care for the automobile part but he goes into depth regarding plane design and aeronautic principles, maybe it's because I was not very knowledgable to begin with in this subject but I find it quite interesting.

https://www.youtube.com/channel/UCynGrIaI5vsJQgHJAIp9oSg

EA story, does interesting maps showing the front lines as they were, he also delves into some lesser known things like the Baltic wars of independence.

https://www.youtube.com/channel/UCElybFZ60Hk1NSjgCf7I2sg