The Unity manual says "sides" actually refer to "left" and "right," not the actual top and bottom of the platform. https://docs.unity3d.com/Manual/class-PlatformEffector2D.html
So even with "Use Side Friction" and "Use Side Bounce" unchecked, the top of the platform (and bottom also, if "Use One Way" is off) will still be bouncy, as long as the physic material is set in the collider.
"Side Angle Variance" seems to have become "Side Arc." Here's an image of what a Side Arc of 45 looks like (along with the Surface Arc at the default 180):
The manual says anything within these areas is considered for Platform "behaviours." Anything outside of those areas will be considered for one-way collisions (i.e. allowing colliders to pass).
Yes the sides refer to the perpendicular portions of the collider. In the video I didn't specifically test out the side features when adding the physic material, so that may have added some confusion. The physic material will always work with the horizontal surface of the collider as shown in the video as long as it's assigned.
If the character were to bump into the platform on the left or right side, or if the platform was moving horizontally it would add a bounce to the player and push them. Had I added in some walls this might have been better explained. Another example of this would be adding in large walls that the player slips off of if they had an "ice" type physic material.