I'm trying, with little success, to downgrade from Big Sur back to Catalina. I have my internal HD backed up to an external HD. Unfortunately I didn't back up Catalina prior to upgrading! Still, it would seem from looking on the web that it is still possible. However a popup is telling me "this copy of macOS Catalina Installer is too old to be opened on this version of OS." My iMac is a late 2015 model. Am I doing something wrong?! Peter
iMac 27″, macOS 11.1
Once the Catalina installer has downloaded, it will try to open which is when you get the "too old" message. Click "Quit". The next thing you need to do is create a Catalina USB Bootable Installer before you erase your hard drive. Either use the instructions on the linked page or: How to create a bootable installer for macOS - Apple Support
Once you create the bootable installer, you will boot from it, erase your internal drive and install Catalina according to the instructions.
Once the Catalina installer has downloaded, it will try to open which is when you get the "too old" message. Click "Quit". The next thing you need to do is create a Catalina USB Bootable Installer before you erase your hard drive. Either use the instructions on the linked page or: How to create a bootable installer for macOS - Apple Support
Once you create the bootable installer, you will boot from it, erase your internal drive and install Catalina according to the instructions.
Thank you "dialabrain." I have been on this page you suggest but may have been overwhelmed by its complexity. Complexity to me that is. I think I have followed instructions but am stymied when they open a page to down load Catalina! A popup tells me it's not possible. There must be a way round this that I have yet to discover.... Peter
I have downloaded to Catalina but I see that I have lost data e.g. my "notes" have been wiped clean! Going from bad to worse I'm afraid. I will keep plodding along and see what happens. Or there maybe a way to get my notes back in Catalina! Let's see
Thank you for your prompt reply "dialabrain." Let me see if I can implement your instructions - I will let you know...
You're welcome.
Downgrading Big Sur to Catalina
