Hello James Besancon, thanks for posting this in our community.
The error you're encountering usually means that BitLocker has entered recovery mode because Windows detected a change or issue during startup. If you're stuck at the BitLocker screen, you can try forcing Windows into the Recovery Environment. To do this, power on your PC and as soon as the spinning dots appear, hold the power button for about 5 to 10 seconds to force a shutdown. Repeat this process twice. On the third boot, Windows should enter the Recovery Environment.
Once you're in the Recovery Environment, you can try using Startup Repair or other recovery options available there.
Kind regards,
John Oli