I wish I could share better news, but the truth is that no one can get the BitLocker recovery key for you, including Microsoft staff or support.
Microsoft states this clearly here: https://support.microsoft.com/windows/find-your-bitlocker-recovery-key-6b71ad27-0b89-ea08-f143-056f5ab347d6
“Important: Microsoft Support doesn't have the ability to retrieve, provide, or recreate a lost BitLocker recovery key.”
The BitLocker key is typically saved to a personal Microsoft account, a work or school account, or it may have been printed, written down, or saved as a file somewhere else. However, those last options would require you to have saved it manually, so you would likely remember doing that.
For a personal Microsoft account, check here: https://account.microsoft.com/devices/recoverykey
For a work or school account, check here: https://aka.ms/aadrecoverykey
At this point, it is a matter of figuring out where and under which account the key might have been saved. Think back to how you used this drive. If it was connected to the computer when Windows was originally set up, the key would usually be saved under the same account used to set up Windows.
However, if the drive was moved from another computer, the key may be stored under the account that was used on the previous computer instead.
Hopefully, this gives you some direction and helps you locate the correct account and recovery key.