I don't think Graphene has any control over this on behalf of apps. It has normal screenshots unless the app specifically doesn't allow them. My banking app blocks them by force and Molly (Signal) does by default but has a toggle.

But software toggles can just be ignored by an OS. You wouldn't know if a closed software was ignoring it, nor could you reasonably verify the source even if you were skilled to.

These privacy switches are a complete farce beyond trust. They may or may not work. I trust that Graphene isn't ignoring them, but they could be. I absolutely wouldn't trust Google one way or the other. But Amethyst should have the toggle either way in my opinion. People could choose. The debate over convenience is totally moot.