What should I call this element? Popup? Dialog? Modal?
If you're using Material, it's considered a dialog and there are types:
We usually call it as non-modal dialogue e.g when hit Gmail compose button, a nonmodal dialogue opens.
Nonmodal dialogue vs modal(dialogue): The purpose of nonmodal dialogue is not to completely block the main window and let the user interact with the main window even if the dialog is there which is not the case for modal.
Popup: pop up is kind of notification with one action button inside (usually). Users don't have to deal with it right away. But the element won't go away unless users explicitly take the action.