Unfortunately, I don’t have CAD models and, I believe, the video linked in the OP was done in Blender, but I’ve seen other teams posting CAD renders of various differential designs in the past. (@ranOOm do you have any Differential CADs?)
The concept behind differentials is rather simple. If you have two motors and two output linked via formula a=x+y and b=x-y respectively, then when motors run in the same direction (x=y) you get power on output (a) and, when motors run in opposite directions (x=-y), then output (b) gets power.
There are plenty of FRC Differential Swerve Drives utilizing this principle:
https://www.google.com/search?q=swerve+drive+differential&tbm=isch
https://www.youtube.com/results?search_query=swerve+drive+differential
I hope these videos will be helpful to visualize how differentials work:
Differential turret by @tabor473
9551A Dual Differential Transmission by @Mr_L_on_Yoshi
The trick is to build the geartrain from the limited set of VRC legal parts such that it is strong enough and any friction losses don’t negate any potential advantages of the increased peak power. It is very easy to overdesign such things.
One of the features of the prototype pictured in the OP is that when everything is properly aligned and motor’ axles don’t touch 393 gears, then configuration “defaults” to an ordinary tank drivetrain. The power from the motors to the wheels doesn’t need to go through the extra geartrain, other than the three 60T gears that it would be going through in any non-differential design that combines power of the two motors into one driving wheel.