Then they deserve you taking a photo with a second phone
I doubt most people have a second phone on hand, ready and able to capture actual screen shots when your phone is preventing screenhots.
However, my idea happens to hit a very new limitation: for some reason, "privacy filters" are suddenly a thing. New phones have them built-in as some new magic display function, and for everyone else, there's this mad marketing push to get people to buy and use privacy foils in place of glass/foil screen protectors.
IDK what's up with those. Since when "shoulder surfing" with smartphones is a real problem, and why do marketers and product designers bet there's so much latent demand for it?
The only thing I could think of is if you want to browse TikTok or Instagram in public and don't want people seeing the weird shit that's on your algorithm, but even then, that's kinda weird.