I've just had some success getting Catalina on HFS+: Please ignore that I selected the APFS volume of my main boot drive on the tester Mac. I hadn't noticed when taking the screenshot and when I did notice I'd already erased the volume for my next test. Method: Code: From an image of a working install of macOS Catalina (/Volumes/Macintosh\ SD/): ditto /Volumes/Macintosh\ SD/ /Volumes/Macintosh\ HFS+ ditto /Volumes/Macintosh\ SD\ -\ Data/Users /Volumes/Macintosh\ HFS+ ditto /Volumes/Macintosh\ SD\ -\ Data/Device/ /Volumes/Macintosh\ HFS+ Ditto merges directories and keeps permission. Verbose mode boot spews out a lot of errors, and I saw high CPU usage once logged in. It eventually quietened down, though. I'm trying again from a fresh, unbooted install made to a disk image, then I will try directly from a macOS installer. Wish me luck!