According to JAR File Specification

Line length:

No line may be longer than 72 bytes (not characters), in its UTF8-encoded form. If a value would make the initial line longer than this, it should be continued on extra lines (each starting with a single SPACE).

However, mx appears to be generating longer lines, e.g.:

Premain-Class: com.oracle.svm.hosted.agent.NativeImageBytecodeInstrumentationAgent

As found in the manifest of svm-21.3.0.jar