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
  

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)