Keep the video call window on top of your other apps: Choose Video > Always on Top. The call window floats on top of the other app windows, so it’s always visible, no matter which app you’re using.
View a video call in full screen: Click the green button in the top-left corner of the FaceTime window, then choose Exit Full Screen or press Control-Command-F.
Temporarily hide the video call window: Click the yellow minimise button Change video effects for FaceTime calls.
Note: In one-on-one calls you can also change the orientation — just move the pointer over the picture-in-picture window, then click What is Screen Time on Mac?