Installation blocked by bitlocker

I faced the same scenario as I try to setup up the dual boot after having received a factory new dell laptop. Turned out for me that the "activation required" step simply is a UI stage as Windows wants me to savely store the recovery key on some media. After having done this and the "activation step" has been completed the device is shown to be encrypted without any processing. So the encryption was already in place, as the disk management and ubuntu both remark.

After activation the GUI shows the regular "device encrypted" screen and options so that the regular guides for decryption can be followed.