Can I download an old version of MACOS
I've just upgraded to Monterey but want to go back to Mojave. Is this possible
MacBook Air 13″, macOS 12.4
Question marked as
It is possible but it involves erasing the system drive completely.
So make sure to have a full backup.
using Safari, go here for getting old installers:
How to get old versions of macOS - Apple Support
You need to create a bootable installer on a usb thumb drive, boot from it, launch Disk Utility, completely erase the internal drive (not just the volumes in it), then run the installer.
When the installer finishes, migrate the user accounts from your backup.