Have you opened a case with HCL yet? According to the docs, return code 57 is
Failure to load a scanner plugin. Possibly corrupt installation. Reinstall or upgrade the scanner
Return code 7 is not documented.
Linux scanning requires the library libstdc++.so.6. Is this present on your Redhat 8.6 box?
Look in /opt/tivoli/cit/logs for log files.