Don't know if the create ISO script works. I'd have to have macOS to use it. Don't feel like booting Windows to use Windows programs to do it.
Just create a 10 GB .qcow2 file, I failed at resizing the one I converted from the img I got with dmg2img. So I just deleted the partition, and made a new one. It's still copying everything from the Installer App folder to the qcow2 image. You need hfsprogs to format as HFS+.
To mount the "BaseSystem.img", use qemu-nbd, instructions for that here. To get the img file, use dmg2img.
Using mount to mount the img file doesn't work for some unknown reason. Doesn't matter if you use an offset or not. According to file, the start sector is 1. Internet says the offset is s * 512, which is 512. The sector size is 512. If you use the start in fdisk, that doesn't work either. Just says wrong FS or something. You can specify hfsplus and it says the same thing.
/dev/nbd1p1 on /mnt/base_old type hfsplus (rw,relatime,umask=22,uid=0,gid=0,nls=utf8)
It's HFS+, that's mounted with qemu-nbd.
Slow because the image file is on a mechanical drive.
Why won't Clover boot with host-passthrough in QEMU? Thought the config I'm using was for Ryzen.