For those just looking for a second screen with their iPad or MacBook, Universal Display does exactly this, given you’re already in the Apple ecosystem.
The built-in MacOS feature that does this called continuity… but I know it was renamed once (used to be sidecar). Maybe you’re referring to an old name? Or is it a product?
Edit: I looked it up and it appears that the app is continuity and “Sidecar” and “Universal Control” are features. IDT those names show up in the OS UX though.