Bitlocker decryption not working

[mmiadmin]

I am trying to use the following to de-encrypty bitlocker that already came with the 128 bit encryption and it is not doing it. Is there a  way to do this, so that I can decrypt while a device joins during Autopilot and then encrypt it with a 256 bit encryption?

$BLV = Get-BitLockerVolume

Disable-BitLocker -MountPoint $BLV

Tried this also

Disable-BitLocker -Mount "E:"

But no luck, any thoughts or suggestions.

[#2]

@mmiadmin But why during autopilot? it can be done at a later stage, too, right? The first PowerShell lines are something I used before. You can start encryption using Configuration Profiles afterward... Why are they already encrypted? (Wiping them and using a Windows 11 USB stick is also an option?)

[#3]

Any update ?