@Alex Kumpan - were you actually able to recover your data? Or was it a clean install which deleted all of the data?
I've got a Dell as well (Inspiron 7300 2-in-1), and the BIOS update on 22/09/2021 activated BitLocker. My problem was I had several years of data on it that I was migrating to another cloud provider, but hadn't completed the migration. If I had to go in and do a clean install or swap out the SSD, I'd have lost all of the data.
On the Inspiron, I had used several @harsh.com accounts as well as an office365 business account, which no longer was active as the business is de-registered and the associated domain cancelled.
The Recovery Key was not in the easy-to-find places (like the @harsh.com .com accounts).
I scoured the forums and read about flashing the BIOS. I was able to revert the BIOS back to an earlier version, but upon rebooting the "BitLocker blue screen of death" was back.
I contacted Dell support and although they were prompt and helpful, the only option (as we couldn't access the boot menu anymore after my many attempts of messing with it) they offered was to swap out the hardware.
I read about the option of the BitLocker recovery key possibly being on Azure. I did discover that my old business account actually did have an Azure profile , but couldn't access it as I first had to update the 2-step-verification option (my old business email which no longer was accessible). After waiting four weeks for Microsoft to activate the changed 2-step-verification, I was able to get into Azure.
Once I got into Azure, I found I needed to go to the Microsoft Endpoint Manager admin center (Microsoft Intune): (https://endpoint.microsoft.com). Once there, I couldn't find the device under the "Devices" tab.
I was about to give up, but scouted around and checked the "Users" tab. There under the user profile associated with my business account there was an option to "Manage Devices". There I found the computer I was looking for and the BitLocker Recovery Key.
And lo and behold, it actually worked.
This morning, when turning on the computer, the BitLocker blue screen was back, but entering the BitLocker recovery key, I was able to log in. I then turned of BitLocker and, once it finishes decrypting the drive, I'll make a backup and do a clean install of the machine.
I appreciate this is a lengthy reply, but wanted to share my story in case it helps one or two others who are facing loss of important data.
And to share another lesson learnt the hard way: backups save a lot of time and hassle.