I have a handkerchief that is really two sewn together along all four edges. One of them has a square hole in the middle.

The idea is to place it over an object on a table so that the square hole envelopes the object. The handkerchief is then whisked away and the small object seems to vanish from the table.

What is this called?

I believe Patrick Page put that out. You are right in how it works.

I think it is called: "The Go-Go Vanisher'... they still can be purchased from various dealers

Duane Laflin has a "vanish cloth" that he uses with a stratosphere type trick.
You can view it here https://laflinmagicstore.com/products/pr......a9&_ss=r

Not sure if he sells the cloth seperately, but it might be worth it to reach out to him.

Mark

Thanks All! That was the information I needed.