In short, it’s a nightmare. The best strategy is to boot Windows, disable bitlocker and then proceed with the factory reset. But I didn’t do that, and I didn’t have the bitlocker key, so completing a factory reset became difficult.
The computer I tried to restore is a 2018 Dell XPS 13.
It comes with a tool called ‘Dell SupportAssist OS Restore’ which can factory reset the computer using an image stored on a disk partition. For reasons unknown, this tool does not work with a Bitlocker encrypted OS partition.
The approach that (eventually) worked for me was:
- Use another windows computer to create a Windows recovery media USB drive.
- Edit the BIOS to boot from the USB drive (I think only one of my USB ports detected the drive, and possible only if connected without a USB hub).
- Use the advanced setup option, delete the Bitlockered partition, create a new partition and choose it as the OS partition (you can’t install over the Bitlocker partition).
This is why I hate computers.