Greetings, arham210.
To start, can you confirm if you are using the following steps?
"Turn off FileVault encryption on Mac
When you turn off FileVault, encryption is turned off and the contents of your Mac are decrypted. The decrypting could take a while, depending on how much information you have stored. However, you can still use your Mac to do other tasks while the information is being decrypted.
- On your Mac, choose Apple menu
> System Preferences, click Security & Privacy
, then click FileVault. - If the lock at the bottom left is locked
, click it to unlock the preference pane. - Click Turn Off FileVault.
- Click Turn Off Encryption." Turn off FileVault encryption on Mac
If so, and the issue continues, try to turn off FileVault in safe mode. Safe mode prevents certain software from starting and could help resolve the issue. How to use safe mode on your Mac
We hope this helps!
Sincerely.