How to downgrade MacBook from macOS Catalina to Mojave.
Upgraded to Catalina
must go back to mojave
Mac Book Pro mid 2012
[Re-Titled by Moderator]
MacBook Pro 15″, macOS 10.14
If your Mac currently boots to Catalina, then the first thing you should do is create a bootable clone of Catalina on an external drive. If something should go wrong after you've erased your Mac - because downgrading the OS will require that - you sill have a bootable macOS system that you can fall back on. Use Carbon Copy Cloner to make that clone.
After you have cloned your current boot drive, then you can:
1• Boot to the external, cloned drive and download the macOS 10.14 Mojave installer app from the App Store.
2• Use Disk Utility to erase the internal drive. Use the APFS format w GUI partition scheme.
3• Double-click the "Install macOS Mojave" app in the Applications folder to reinstall Mojave on the internal drive.