Hello!
BitLocker locked your system because it identified a hardware change. The TPM on your new motherboard is different, causing the system drive to be locked as a security measure.
First, make sure this is the correct recovery key. It may belong to another device, an old device, or be in a different email address.
The BitLocker Key can be in any email. Check all your personal emails. Also check if any Google (Gmail) or other domain emails have the Key linked to them. Emails from other domains can also be Microsoft accounts.
- When you log into Windows or any system application using a different domain account (such as Gmail), Microsoft creates a Microsoft Account for you using your email.
- Go to the website below > Log in with one of your emails > See if the Recovery Key is saved in the Email.
https://account.microsoft.com/
- If you can't find your Recovery Key, log out of the Account and log in to another one.
- Also log in with your Google Account or another domain account that you have used in any Windows application.
- If you get the message that the account was not found, go to the websites below and see if one of them works.
https://myaccount.microsoft.com/
https://mysignins.microsoft.com/
https://azure.microsoft.com/en-ca/account
- Sign in with emails of family members who are with you. Sometimes the Recovery Key may be in one of their emails.