“ The most intransigent problem with failed EFI firmware updates has been with the iMac Retina 5K 27-inch Late 2015, or iMac17,1. Some have sailed through updates bringing them to version 428.0.0.0.0, others remain firmly stuck at 170.0.0.0.0, which was current for macOS Mojave 10.14.6 in July 2019.”
The first time I tried to update my late 2015 27” iMac, it bricked the system, and I had to reinstall from Time Machine backup. I gave up on updating for quite some time, every day having to dismiss the reminder to update. Recently, I was able to update to Catalina. It was painful and took multiple tries, but eventually it got there.
The first time I tried to update my late 2015 27” iMac, it bricked the system, and I had to reinstall from Time Machine backup. I gave up on updating for quite some time, every day having to dismiss the reminder to update. Recently, I was able to update to Catalina. It was painful and took multiple tries, but eventually it got there.