Thanks @BearWithBeard it is working now.
And finally, sha204_lib_return_codes.h and sha204_library.h can be obtained from the Security Personalizer sketch. If you're going to copy and paste those files into the Arduino project folder, you may need to replace the <...> brackets around the included file with "..." (e.g. #include "sha204_library.h"), or else the IDE might not find them.
I forgot I had to change the <...> brackets around the included file with "..." for the referenced libraries when copied locally. I also got platform.io setup so I'm going to transition to using it going forward in order to help pin the dependencies.