I have tried this before on my wallet app, but it just displayed a blank image. Though I didn't have any money inside. I also tried on another one and it gave a notification that this action is not allowed. I don't know but I feel like this feature will not stop some stubborn people. Since their phone will not screenshot, they will just use another phone and snap the screen. And it is only going to be their fault if they steal their money.
One of the reasons why they disable screenshots on some wallets is because of security reasons. Some users can be very ignorant and don't like to take their security seriously, and aside from even using another phone to snap the wallet phrase, they can easily copy and paste the wallet on their notepad and still take a screenshot of it. That's for wallets that 's for wallets that allow phrase copying. Some people also use their hands to write down the phrase on a piece of paper and still make the mistake of snapping and saving it on their phone where other eyes can easily access it without them knowing.