I am a lifelong fan of the boxer engine. The horizontally opposed boxer powerplant has been behind most of my favorite cars and motorcycles of all time.
A boxer differs from an in-line motor, in that the cylinders are horizontal as opposed to vertical, and this provides many benefits described in the video.
Smooth, incredibly linear torque throughout their power range, easy to cool and maintained in their simpler forms. Absolutely daunting and unapproachable far above most owner's maintenance skillsets in recent model flat-six Porsche applications, the boxer sounds like an engine should and puts the power down.
It was even fun in the Vanagon.
The gentleman does, additionally, burn some time discussing in-line fours. I think he needed them as a counter-example. As the YouTuber explains you can crank a lot of power out of an inline 4, but I think the case is made for the boxer.