If output of first command shows 64-bit architecture, then use installation scripts from following post.
NOTE: Installation by scripts is a lengthy process and takes some time. Please be patient and let the script run till it announces it has completed its job.
My repo which you tried and failed is provides packages for Debian 11 AMD64, while your Rock 4 and OS require packages for Debian ARM64. That is why you got the above responce.
The scripts will detect the OS and architecture, and will build matching packages right on your Rock.