Warning: Firmware change

[maverick100]

Just a little warning; Firmware is changed. 2018 iMac 27"; Firmware was changed when I installed the Beta on an external drive via Thunderbolt 3. I have run into a variety of issues when trying to go back to Mojave on the internal drive. Internal drive was wiped; and did a clean install of Mojave. Unable to select item in System Prefes; unable to remove notifications from TM. Lesson Learned. Will never run a Beta or Test OS on my production iMac. My fault.

 

[pldelisle]

This has nothing to do with the firmware ....

 

[flowrider]

I'm on a NcMP and have none of the issues you are experiencing. I have two more SSDs with Catalina (10.15.6). I am able to toggle back and forth, between OSs on a restart without incident.

Lou