The cabextract utility used in the process to create the ISO was recently updated in Homebrew, and contains a bug which causes this.
To work around this, see Appendix D of the Unofficial Fusion 13 for Apple Silicon Companion Guide version 9.1 (it was just updated) that @scott28tt linked you to. Use that procedure to build and install an older version of cabextract that works.
The developer is aware of this bug, and looks to have checked in a fix for it in the development version. It looks like when that version is released this will no longer be an issue.
- Paul (Technogeezer)
Editor of the Unofficial Fusion Companion Guides
