My friend was interested in HOI IV (he played it a bit and we did one coop game).
These were the tutorials I suggested.
By far the best is by this guy Quill18 who also streams Stellaris, Civ, and number of other strategy games.
This is his tutorial.
https://www.youtube.com/watch?v=bNUhKQ4hxUsro
You can also check out a couple other like this Japan one.
https://www.youtube.com/watch?v=08AGiCdaL2U&t=112s
