It's an American accent, but with rhotacism, a type of speech impediment. He sounds vaguely British at times because of the tendency for "R" to come out sounding like "W"

https://en.wikipedia.org/wiki/Isaac_Arthur

Thanks a lot. I wasn't aware of this speech impediment and how it causes the vaguely British at times.

I actually have the same impediment but never knew the term `rhotacism` - thanks!

It's a speech impediment; he has trouble saying R's (and has improved as he's narrated more and more videos).

Isaac's earlier videos would show Elmer Fudd with the message "Having problems understanding me? Turn on CC." Example: https://youtu.be/gOu3zGfP-TQ?t=40

Source: I've watched lots of his videos and highly recommend them—mind expanding ideas!

Thanks a lot for the context. I have to say I didn't really have a hard time understanding him. I didn't even consider the possibility that it was a speech impediment.

American, but he has a speech impediment.

I was going to ask the same question, its so unusual but never heard it before

as a native english speaker I would guess dutch, norwegian, swedish or icelandic