unable to decrypt filevault drive

Hello Ed Killian-Keup,

Thank you for using Apple Support Communities! I understand that you're wanting to turn off FileVault on your Mac, however decryption does not appear to be proceeding past 2 hours remaining. You've come to the right place for help.

I would like to have you restart your Mac in macOS Recovery to access Disk Utility:

Repair a disk using Disk Utility on Mac - Apple Support

Ensure your startup volume shows as mounted, then follow the steps in the above resource to run First Aid on your physical disk, container, and volume. Once that process is complete, restart your Mac. You'll want to ensure that your Mac is awake, logged in to a user account, and plugged in to AC power for decryption to complete as noted here:

Use FileVault to encrypt the startup disk on your Mac - Apple Support

Keep us posted if there's any change after trying those steps.

Cheers!

Unless someone else has a better idea to get you unstuck at this point, if this were me at this point I would go ahead and try to make a Time Machine backup to an external USB drive, then restore that via Time Machine backup via Recovery Mode as that will erase the drive completely removing any corruption restoring the data on a clean file system.

The only question really is whether a Time Machine backup would be able to run if the partition state is unhappy enough for First Aid to fail in the first place.

How much free space do you have on that partition you are trying to disable FileVault on? You really want a minimally decent amount of free space before you start the process to disable FileVault. (10 gb minimum would be my recommendation)

I would then try again to boot up in Recovery Mode (COMMAND-R during boot up), go into Disk Utility, and Mount the drive with the password, and run First Aid to see if that helps.

You can also try this using Internet Recovery Mode (OPTION-COMMAND-R).

Hi Ed Killian-Keup,

Thanks for getting back to us with the results and I would like to have you reach out to Apple Support next. You can reach them using the link below:

Apple - Support - Product Selection

Take care!

If it is a snapshot issue, then perhaps deleting the snapshot will fix the problem. You need to launch the Terminal app located in the /Applications/Utilities folder and use the "tmutil" to delete the snapshot(s). "tmutil" is a Time Machine command line utility. I've only just started experimenting with this utility and I'm not a Mac now so I cannot provide further guidance. Perhaps another user here can assist or you can search online for an article which provides some background information and examples on how to list and delete snapshots.