Can I downgrade OS on Mac?

Unfortunately downgrading to an older version of macOS (or Mac OS X as it was previously known) isn’t as simple as finding the older version of the Mac operating system and reinstalling it. Once your Mac is running a newer version it won’t allow you to downgrade it that way.

Can I downgrade from Catalina to High Sierra?

But first, if you want to downgrade from macOS Catalina to Mojave or High Sierra using a bootable drive, follow these steps: … Open System Preferences > Startup Disk and select the external drive with your installer as the startup disk. Click Restart. Your mac should then restart in Recovery mode.