Create a Bootable USB Stick from an Older Version of macOS

Download the version of the OS you want to install here: https://support.apple.com/en-gb/HT211683

Open InstallMacOSX.dmg by double-clicking.

Double-click on InstallMacOSX.pkg

The installer runs

If you don't get the following error: "This version of OS X/macOS cannot be installed on this computer."

Wait for the end of the installation and follow the following tutorial : How to create a bootable USB drive

Otherwise, go to the next step.

Quit the installer and drag and drop the InstallMacOSX.pkg file on your Desktop

Open Terminal and enter the following command: "cd Desktop"

Enter the following command: "pkgutil --expand /Desktop/InstallMacOSX.pkg FolderName" (You can change FolderName to any name you want)

A folder with the name you gave appears on your Desktop.

Open the folder appeared on the desktop.

Open the "Distribution" file with TextEdit.

Look for the line with "var platformSupportValues"

Let TextEdit open and go to the Terminal and enter the following command: "ioreg -l | grep -i board-id"

Copy "Mac-XXXXXXXX"

Go back to TextEdit and after the symbol "=" and in the brackets paste "Mac-XXXXX" and add a comma ","

Save and close the file

Go back to the terminal and type the following command: pkgutil --flatten FolderName New.pkg (FolderName = the name of the folder and New.pkg = the new .PKG file that will be created)

Press enter and wait for the file to be created

Launch the new .PKG file

Congratulations you can launch the installer.

To continue creating the USB Stick follow the following tutorial : How to create a bootable USB drive