I am getting "the disk Macintosh HD can't be unlocked" popup error after reinstalling Catalina.
I checked Disk Utility, there are 3 partitions named, "Macintosh HD", "Macintosh HD - Data", "Macintosh HD - Data Data".
How can I fix this?
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If you can still boot into the Recovery or Internet Recovery please open the Terminal app from the Utilities folder and copy the result of
diskutil apfs list
It is likely there was an issue with the install/migration and depending of free space you might have to erase and reinstall the OS (for that please follow the Apple guide at https://support.apple.com/guide/mac-help/reinstall-macos-mchlp1599/mac)
Editing the name of the drives so they are unique will help you know which is which.
This same thing happened to me. I had:
Macintosh HD - Data
Macintosh HD - Data - Data
One thing that has changed that I didn't know with Catalina is that when you look at Disk Utility it shows
That version (Macintosh HD) was greyed out for me. I couldn't First-Aid it, delete it, mount it, nothing.
I found that if you go to:
View > Show All Devices
It will show you
APPLE SSD <some serial number> Container disk2 Macintosh HD
If you select that top node, (APPLE SSD), and then click erase and put in:
Name: Macintosh HD Format: APFS or Mac OS Extended (Journaled) Scheme: GUID Partition Table
Then it should ask for your AppleID Password and then it will delete the volume
Then you can proceed with the reinstall like you normally would.