@Beyondspace I am having the same issue!
My site is: https://rrs.squarespace.com
You can see the blue video overlay has the clipping path applied, but not the video itself.
This is the code I am using:
section[data-section-id="6120187c92e3823b1c2462bd"]{
clip-path: polygon(100% 0, 100% 50%, 50% 100%, 0 50%, 0% 0%) !important;
}