I've met this problem last week. I had my 2018 MBP repaired and after it was returned, I could not install Big Sur beta5 anymore. I tried to reset SMC PRAM, all failed. I've called Apple's developer support and Apple customer support, they all said the they do not support any Beta system. Then I saw this post and thanks macguy59 and RobChag's solution, I recovered the firmware of T2, after long waiting for network recovering, now I finally installed Beta 6 on my MBP! Thanks a lot!
billxiong
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution
Last seen
User for
Post
Replies
Boosts
Views
Activity
Just the same problem, can not install beta 5 and beta 6 also
I learned from Parallels forum that the problem was caused by version check of Parallels.
The solution is first set the environment variable "SYSTEM_VERSION_COMPAT=1" , and then use command 'open -a "Parallels Desktop" ' in terminal to run PD. Now PD15 can start