Short answer:
There is no reliable way to detect screenshot.
Long answer:
There are several ways the operating environment captures what is being displayed; this is true for both Windows and Linux and Macos. Not all ways generate interruptions, and the vast majority of these are not monitored by browsers.
What you see when you take a screenshot while watching Netflix is the result of another technology: DRM (digital Rights management, or digital rights management). A screen capture function includes only content that is not marked as safe.
An integration between the streaming (adding DRM to the content), the browser which displays the stream (which marks the areas of the screen that are displaying content with DRM) and the operating environment (which identifies displays secure that have encryption technology between the video source and the device) allows you to view the content, but prevents copies by OS for processes that are not part of the rights management chain.
Possible duplicate of I need to lock Ctrl+v in a text box
– Ricardo Pontual