can I uninstall mohave to catalina so my older apps work

mbluett Said:

"can I uninstall mohave to catalina so my older apps work"

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Yes.

If macOS 10.14 Mojave or earlier was installed when purchasing your Mac, then you can downgrade to Mojave.

Here is how I would go about doing so. Perform the Following, in the order provided:

1. Create a Time Machine Backup -- of the current install
2. Install Mojave -- using a USB Installer
3. Use Migration Assistance -- to transfer current installed items over to the new install.

Or... If an applicable option, then just restore the Mac to Mojave from a Time Machine Backup

mbluett Said:

"can I uninstall mohave to catalina so my older apps work"

-------

Yes.

If macOS 10.14 Mojave or earlier was installed when purchasing your Mac, then you can downgrade to Mojave.

Here is how I would go about doing so. Perform the Following, in the order provided:

1. Create a Time Machine Backup -- of the current install
2. Erase Hard Drive: Go Here
3. Install Mojave -- using a USB Installer
4. Use Migration Assistance -- to transfer current installed items over to the new install.

Or... If an applicable option, then just restore the Mac to Mojave from a Time Machine Backup

Several things have changed in the file system in Catalina, so the steps to revert to an earlier OS need to be followed exactly or they may wind up with 2 Mac HD - Data folders (and a corrupted install). This is especially important when trying to revert to an older OS version - but also when simply trying to reinstall Catalina since you can also wind up with 2 Data volumes.

https://support.apple.com/en-us/HT208496

Revert your Mac to a previous macOS version - Apple Support

Remember, you must erase your internal drive before you can do anything, so you need to have a backup made before you upgraded which includes the OS and all your files. And you must use recovery to erase the drive and reinstall - a USB installer will most likely not work in this case. Read the Apple article Barney linked to.

The only other way (if you do not have a Time machine backup) is to have a bootable external clone with the previous OS on it. You can boot from that, wipe your internal and then simply clone back your entire system.