Hmm, you may need to use a FScreenshotRequest for that to work then, which requires a smidgen of C++. You can build a C++ plugin that’s nothing but a Blueprint native function library, and then do the necessary in there.
request->RequestScreenshot("ScreenShot", true, false);
Assuming you have Visual Studio installed, and know at least some C++, it’s really quite easy to “add C++ class” and choose blueprint function library and then implement a single static function to do it.