... Little to no instruction on what to do internally. ....The secrets protect themselves, it has to be felt, blah blah blah cryptic IP talk.
To take this out of the "secrets...blah blah... cryptic" department -- and to point out a relatively accessible "feel" mentioned in the video -- rather straightforwardly at 1:22-1:44 -- it is pointed out that as correct internal structure becomes external movement
: "All movement is done as if swimming in the air."
To interact with water in swimming -- particularly in treading water (the closest aquatic thing to zhan zhuang) -- requires
a definitively different grasp of internal structure to support movement than what most people operate from when they just move around out of water.
People who have not grasped this necessary alteration of structural support when trying to swim mostly thrash water, ineffectually or at best inefficiently, and, generally, sink in sad bewilderment.
But the physical lesson is DIRECTLY applicable -- people just don't realize that connection and how to adapt it. The dynamics of treading water are closely allied to actual movements in aikido that flow from structure. That provides a much more commonplace and perhaps more relatable way to see this supporting structure driving the mechanics of effective action.
Viewing the gentleman's examples in the video with that basic structure/dynamic overlay in mind makes what is being done far more understandable.