I am facing a little nightmare here after trying to update a FileVault-encrypted two-port 2017 Macbook Pro from Mojave to Big Sur.
During the update the following error ocurred: An error occurred preparing the software update.
There were not many options at this point. A restart led to the login screen. After successfully logging in the update was again attempted with the same error.
The UI tells me that at least parts of Big Sur have been installed.
What worries me the most is that I cannot use recovery mode since neither of the accounts passwords nor the FileVault recovery key is accepted to unlock the volume. (also not possible in target disk mode via another Mac – error: The supplied password failed to unlock the disk.)
I also tried (among other things) booting into internet recovery and SMC-, NVRAM-Resets with no luck. Single User Mode with access to terminal seems to be no longer present on this OS version.
After all this messing around the update is no longer attempted when logging in. The screen just turns black and the Mac restarts, leaving me in an infinite loop.
Is it possible the Keychain that holds the FileVault encryption info is damaged/gone?
My backup on a network share also seems to be borked. (sparsebundle damaged)
I have been trying to get my employer to provide an external SSD to make a bootable clone (like I do on my personal machine) for quite some time before this all happened which will probably finally happen now that it’s too late.
Next steps on my list are cloning the drive, trying to (re)install the OS via a USB drive and if nothing helps trying to erase the Mac, losing all data, keys, notes …
I would be greatful for any tips helping to recover the machine with my data on it.