We recently upgraded our winPE version. While trying to install Windows Server 2019 Datacenter, the install fails immediately with the error Windows could not apply the Windows PE bootstrap specified in the unattend answer file. Afterwards, I checked the drive and it never even got to the point of formatting, which we do via the answer file.
Release : 8.5
The error: Windows could not apply the Windows PE bootstrap specified in the unattend answer file happens when there are incorrect settings in the Unattended XML file. In this case the Boot Drives listed in the XML was incorrect and also the License Key was not for the intended Windows Server version (2019 Datacenter) but instead was for the Standard version. After resolving these two issues the image was successfully deployed.