It works fine. I made it build on Github actions: GitHub - JohnAZoidberg/CrScreenshotDxe at gh-actions
You load this onto a filesystem with a uefi shell and you run the command load fs0:CrScreenshotDxe.efi which then installs the hotkey. Then you can run exit to go back to to the main UEFI screen.
Then you press CTRL+ALT+F12 and you get a screenshot on your disk.
