The values of "--app-content" and "--mac-dmg-content" options are lists of paths. The standard path separator character is a colon (:) on Unix and a semicolon (;) on Windows. However, jpackage uses a comma (,) as a path separator. See [1], [2], and [3].

Documentation and cli help are consistent with this behavior.

[1] https://github.com/openjdk/jdk/blob/0e725c6fb1f324b0fd17d206806b4104dc7ba767/src/jdk.jpackage/share/classes/jdk/jpackage/internal/StandardBundlerParam.java#L423
[2] https://github.com/openjdk/jdk/blob/0e725c6fb1f324b0fd17d206806b4104dc7ba767/src/jdk.jpackage/share/classes/jdk/jpackage/internal/StandardBundlerParam.java#L414
[3] https://github.com/openjdk/jdk/blob/0e725c6fb1f324b0fd17d206806b4104dc7ba767/src/jdk.jpackage/share/classes/jdk/jpackage/internal/DeployParams.java#L344