Hello, thank you for reaching out to Microsoft Q&A.
May I please know if you have signed in with your Work or School account on the device? If so, the key might be linked to your Organization account, where you can contact your IT admin to find the key and unlock your device.
Or do you remember how you activated BitLocker earlier? Using a USB drive or a printout?
If you are unable to locate the BitLocker Recovery key, you will need to create a Windows 11 USB Bootable Installation media from another PC and use that media to reinstall Windows.
Reference:
https://www.microsoft.com/en-us/windowsinsider/cleaninstall
Note - Reinstalling Windows will wipe all the data on the HDD.
Let me know if you still need more help.