Whatsapp has long had a Snapchat-like feature for sending photos and videos that can only be viewed once before they are automatically deleted. Until now, nothing has stopped users from saving them as screenshots or screen recordings anyway, but it will soon be over.
About the WA beta in particular it reports that the latest beta version of Whatsapp for iOS stops screenshots and screen recording while the content that can only be viewed once is open. If you try to take a screenshot, you will instead receive an error message informing you that the feature has been blocked for privacy reasons.
This is reminiscent of how screenshots taken with some streaming services simply end up as a black image, possibly with subtitles, although the techniques are obviously different.