Carbon When I boot my Pixel 6a with current GrapheneOS the bootloader says something like this: "Warning! You're booting a different operating system!" and shows a crc/fingerprint/hexcode.
That's exactly what you want to see, and means you've installed GrapheneOS correctly. That's your phone telling you that's you've installed a different OS (GrapheneOS, as opposed to stock Android), and that the GrapheneOS you have installed passes verified boot.
Checking the boot key hash on that screen is one of the post-installation steps. I strongly recommend that you complete all of the post-installation steps including that one: https://grapheneos.org/install/web#post-installation