@freddiemercurystwin - those aren't "table clamp force screw clamps" (effing Chinglish!), they are
fretwork clamps, and from memory were available in 1in, 2in and (sometimes) 3in sizes, but they are really weak and bend very easily (being made from bent mild steel strip and designed to hold only small light pieces of timber or thin plywood whilst it is sawn with a fretsaw). I think they would be utterly useless to hold anything of any size or weight for any length of time without the jaws opening, after all they are only thin, bent mild steel
The nearest thing I can think of which are strong enough to potentially hold any amount of weight are those machine clamps with cast aluminium bodies where the top of the "G" is an 8mm diameter rod and are designed to go into an 8mm hole drilled into the edge of something like 18mm MDF
One difficulty is that I don't think these are made any more (Elu disappeared about 22 years ago and deWalt ceased selling these maybe 15 years back when they stopped selling the Elu-designed router tables). I for one have been unable to find an alternative manufacturer, although there surely must be one (in Germany). A modern equivalent might be the saw guide rail clamps such as these cheap ones from Evolution:
What you can't see in the above photo is the long, flat top of the "G" which is hidden inside a slot in the guide rail. To hold a sheld ther would need to be a hole drilled through the platform (no need for anything fancy, cats really aren't that fussy in my experience)
The issue, however, might be weight and overhang. The greater the weight of the cat and the greater overhang of the platform, the bigger and stronger the clamps will need to be. Frankly, I'd just make the platform out of 18mm MDF so that it runs right across the window board to the window and I'd screw through it into the window board with 3 or 4 no 4.0 x 40mm screws, as
@foxhole recommends. When you leave, unscrew it, fill the holes with 2-pack filler and touch in with a bit of gloss paint
