hi, I just purchased a new computer with Catalina, only one backup performed on my portable hard drive. How can I down grade to High Sierra or Mojave. Catalina is my only backup.
iMac 27", macOS 10.15
The general rule of thumb with macs is you cannot downgrade it to an earlier OS than the one it came pre installed with.
However as Catalina is still pretty new, the chances are it may be possible to go back to Mojave as your iMac was probably manufactured in the Mojave era and upgraded to Catalina on the new OS's release.
The first thing to do would be to make a full back up of your mac while it is running Catalina. This is in case you have to go back.
Next download Mojave from here, How to upgrade to macOS Mojave - Apple Support see Section 4.
When the download finishes you should find Install macOS Mojave.app in your Applications folder. Use that to create to
a bootable USB installer, How to create a bootable installer for macOS – Apple Support If you get an error here it may be an indicator that Mojave cannot be installed on your mac.
If you do get the bootable installer made on this mac or on another then you would boot to the USB installer by restarting your mac whilst pressing and holding down the option/ alt key, until you see the Startup Manager, a graphic display of the bootable drives on your mac, select the bootable USB and press Return.
On restart your mac will display a Utilities window click on Disk Utility, click on View in the menubar and select Show All Devices, highlight the Disk not the indented Catalina Volumes. Now click Erase, give the Disk a name, Format: APFS and Scheme: GUID Partition Map, press Erase. This will now reformat the drive for install. Quit Disk Utility and now click on Install OS, see if it will allow the install of Mojave, if not you will need to use the option to restore from Catalina.
The only thing is doing this if it is successful will probably invalidate your warranty.
In fact it may be worth you trying to download Catalina and making a bootable USB installer in case everything goes
pear shaped, How to upgrade to macOS Catalina – Apple Support
See if other people respond with other opinions and advice before making any decisions.
You can't downgrade to an earlier version of macOS than your computer shipped with.
Thanks for replying, with all that being said maybe I should leave it alone. Thank you.
Told you. 😎
FWIW, Catalina was released at the beginning of October. So if you bought your Mac since then it is unlikely you could downgrade to Mojave.
Down grade back to High Sierra or Mojave on a new computer.
