I have the error Exception in thread "main" java.lang.UnsupportedClassVersionError: com/rarchives/ripme/App has been compiled by a more recent version of the Java Runtime (class file version 61.0), ...

according to the line this version of the Java Runtime only recognizes class file versions up to 52.0 you are running older version of java. to run komga u will Java version 17 or newer.