Make sure at least one Encryption user name is created and assigned to a client system to activate Drive Encryption. Also, disable the BitLocker when you activate Drive Encryption.
Troubleshooting Drive Encryption activation failures start with the evaluation of DriveEncryption.log (C:\Program Data\Trellix\Drive Encryption) and Drive Encryption activation failure event IDs. For details about event IDs, see KB84622.
Below are the troubleshooting scenarios for Drive Encryption activation failures.