Install OS X High Sierra without converting to APFS file system

install-osx-high-sierra-command-line.sh

# create a USB installer
# https://support.apple.com/en-au/HT201372

Download the OS X High Sierra installer via the App Store, it will be installed into the /Applications directory
If it opens automatically, close it
Insert a USB stick (8GB+)
Run the following command where MyVolume is the name of the USB volume:
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

# boot the USB installer

Boot the computer holding the Option key
Select the USB installer as the startup disk

# from the menu, select Utilities > Terminal
# install without APFS (optional)
# use the installpackage parameter to install an extra .pkg (optional)

/Volumes/Image\ Volume\Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall \
  --volume /Volumes/Macintosh\ HD/ \
  --converttoapfs NO \
  --applicationpath /Volumes/Image\ Volume\Install\ macOS\ High\ Sierra.app \
  --agreetolicense \
  --installpackage extra-package.pkg
  

Hmm I did try that, and got this error lol Error: This Mac can only install macOS on APFS-formatted drives.
I think maybe because my system is Big Sur?

The old vicious circle. I'm not sure mate, outside my experience at this point. Try the Ask Different Stack Exchange perhaps. Those guys are pretty smart sometimes.

https://apple.stackexchange.com/

Thanks for all your help @peacefixation, I'll give that a try!

hi, i have 2 SSD´s in my imac 27 2009, on one running High Sierra APFS, on the other one a HFS formated backup of it.

after 10 installations i could finally install HS in HFS, dont ask me how, i forgot :D

BUT when i try to rebuild my system from the timemachine backup (HFS SSD) wich was made under APFS, is AGAIN installs APFS

im getting crazy

"Target is not convertible to APFS: You may not install to this volume because it can not be converted to Apple File System. 2021-02-18 08:31:57+00 MacBook-Pro osinstallersetupd[4322]: Disk disk5s2 is not suitable because DMError: -69837`" ~dangerdave777
I am getting a similar message in my log like this one and I am wondering if you were able to resolve this, and if so, how you managed it?

#jiltedflower ... try to start under safemode and type under terminal

/Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall --applicationpath /Applications/Install\ macOS\ High\ Sierra.app --agreetolicense --converttoapfs NO --nointeraction

(in my case)