There are at least two versions of the headrest mechanism. My 2016 Euro version is very easy to remove :
but the various US versions seem much more difficult because they lack the button on the base. If the button is there on the base plate, then you just push it and this releases the prongs on the headrest (as in the video).
If the base plate button isn't there, then you have to either (i) pull hard on the body of the headrest and it will fly out or (ii) access a small retaining clip in the base unit and release that.
There's a long thread dedicated to the topic of
rear headrest removal that goes into the detail of how other US owners have managed to sort this out.
Bear in mind that the roll-over plates sit just behind the rear headrests (pointed out in the video above). In the case of an impact (even if the car stays level) these roll-over things have a very strong mechanism that forces them upwards, to protect the passengers' heads. Without the headrests in place, your passengers' head could be badly injured if they activate. So it's important to replace the headrests if you give a lift to rear passengers.