Can't turn off FileVault
I tried to upgrade from Mojave to Big Sur on my MacBook Pro, but apparently I can't do that because my disk is password-protected ("You may not install to this volume because it has a disk password"). I tried to turn off FileVault, but nothing happens when I click the "Turn Off FileVault…" button. There is a message further down the window that says "Some users are not able to unlock the disk Main Disk." with a button that says "Enable Users …" - nothing happens when I click that button. I am the only user on the MacBook, with Admin privileges. Any suggestions? Thanks.
MacBook Pro 15″, macOS 10.14