This is phone OS developer's fault for even allowing it. When I take a screenshot, I expect to have an image of exactly whatever was displayed on the screen at the time. Its not a picture of your app, its a picture of my screen. Some banking apps used to (or still) prevent this and now some apps get a hook to insert their branding. My device serves some master other than myself.
This exists for a very good reason. It’s so if an app is showing a password or bank account number or other piece of sensitive information it doesn’t accidentally end up in a screenshot. I think there are other places sensitive information won’t show. Bluesky, and apparently others, are abusing the functionality for advertising purposes. I think it’s a good thing it’s there. This functionality should be easy for apps…
As it is, it is just an annoyance that requires you to do stupid workarounds like taking a photo of your screen.
Imagine if a password manager didn't allow you to copy the password since you might accidentally paste it somewhere incorrect.