had Same issue MacBook Pro 2014 13 inch
it actually changed my FileVault password after I tried to reinstall Catalina with internet recovery.
This happened me to during the Big Sur update on late Thursday when upgrading from Catalina.
See link as it’s apparently happening to Mac’s of a certain year.
https://www.macrumors.com/2020/11/15/macos-big-sur-update-bricking-some-macbook-pros/
I have a Mid-2014 MB Pro.
I did a CCC clone and TM backup before this happened.
During the Big Sur install it restarted to a black screen when it restarted.
Didn’t even see the installing happen yet when this happened.
I tried everything and still wouldn’t continue the update. Just stuck on the black screen.
Holding option key didn’t work with USB thumbdrive installer when restarting and
zapping PRAM worked at the beginning but later in the troubleshooting process it didn’t work. No keyboard commands worked except resetting SMC and internet recovery if I restarted many times while resetting SMC.
I was able to boot into internet recovery mode if I did an SMC reset a few times.
I tried to reinstall Catalina and got it to finish but wasn’t easy.
I was able to startup the mac and see the desktop after that but I may have had to force shut down and SMC reset a few times perhaps.
After that, i restarted the mac and it still kept booting to black screen.
I tried to update to Big Sur but I couldn’t
do that because when it got to the point to install, it didn’t recognize my FileVault password anymore and couldn’t login with both accounts.
When I initially started the Big Sur update it did accept my FileVault password but not after I reinstalled Catalina.
It couldn’t mount the data partition to do the install. It seemed in disk utility the system volume was mounted but not the data volume. When I tried to mount that it asked for my password but it wouldn’t accept that or accept the other accounts password.
When I picked up my shiny new iPhone 12 pro max at the apple store the next day I had apple level 2 support on the phone while waiting in line at the Westfield Century City Mall in Los Angeles.
They didn’t know anything about this issue but i told them I was just going to wipe it and restore from a backup.
That night, after several attempts having to reset SMC as it wouldn’t do anything without doing that, I was able to get into internet recovery using command, option, R.
Using Disk Utility I formatted with Mac OS extended journaled. Didn’t format as APFS as I knew it would convert it during the install.
I installed Catalina successfully (as Big Sur is not available yet with internet recovery) but every time it restarted it went to the black screen so I forced it to shut down holding the power button and reset SMC. Did this a few times until I saw the keys light up and the apple logo with the progress bar and then the install continued. Had to do this several times until the install was complete as it always restarted to a black screen. I did wait to see if it would continue but the black screen persisted for a long time.
The same thing happened when I updated to Big Sur after that but I just did the same thing. shut down and did an SMC reset to get it back to installing.
After the install of Big Sur it started up and I set it up and finished but when I would restart the mac it still went to a black screen. The screen was dark but illuminated a tiny bit like before.
I tried several times with the same result.
After talking to an Apple Consultant friend on the phone the next day about this issue he asked does it startup now.
I tried it and it started perfectly and is starting up normally every time now thankfully. I was going to call Apple but thankfully I don’t have to. I guess letting it sit overnight cleared up the issue magically 😎👍🏻.
I am thinking it was some power issue maybe. I don’t know.
I am very happy it’s working now. I am sure there are many people with bricked MacBook Pros. Hopefully they did a backup.
