Hi,
It is not you. This is a server-side issue and we have gotten many reports. I can assure you the key is saved; you just cannot access it due to a bug. Hopefully, in the next day or two, it will be solved.
A friendly reminder that this is a community support forum where users help other users. Advisors participating here cannot make changes to Microsoft services or access internal systems and can only provide technical guidance, independent of Microsoft's Policy decisions.
https://learn.microsoft.com/en-in/answers/questions/5958929/unable-to-view-bitlocker-keys
I hope this information helps. If you have any more questions, don't hesitate to reach out.