> Downgrading danger

After running Catalina public betas, I want to downgrade to Mojave. Is doing that going to be straightforward?

That depends on your Mac’s hardware. Although it’s time–consuming to perform a clean install, erasing internal storage and installing macOS 10.14.6 should be fairly straightforward if your Mac doesn’t have a T2 chip.

This gets more complicated if your Mac has a T2 chip, because of its firmware. In theory, downgrading it to Mojave shouldn’t result in the installer attempting to download and install an older version of BridgeOS, or iBridge, the firmware which runs on the T2. However, some users downgrading from beta versions of macOS have reported that this can run into problems. These would normally be solved by performing the elaborate procedure to restore T2 firmware, which requires a second Mac and a copy of Apple Configurator 2. This process is detailed at bit.ly/ml163t2rst.

At present, Configurator is unable to solve this problem. The T2 firmware which it tries to install in this situation is not that provided with the beta version of macOS, but the current macOS release. As it can’t perform a firmware downgrade when that would be called for, the restore can fail, leaving that Mac bricked. The only way forward from this is to return it to Apple to be fixed.

This should be resolved in the full release of macOS Catalina, or by Apple ensuring that Configurator doesn’t attempt such a firmware downgrade. However, until this situation is clearly resolved, you shouldn’t put a T2 Mac at risk of an attempted firmware downgrade. For the moment, it’s safer to upgrade.