New Thinkpad T15 w/Office 365 and bitlocker unlock at startup every boot

Never heard of that.  We update BIOS on hundreds of machines with Office 365 and have never experienced any problem.  I will check on this machine if someone updated the BIOS, but unlikely.  As I had updated the BIOS just two weeks before the problem (New laptop for new user).  

This has nothing to do with Office 365.

Someone enabled Bitlocker (on laptops, they SHOULD!)  But then, without suspending BitLocker, they updated the BIOS.  (Possibly).  THAT caused this issue.

This is from Asus but it doesn't mean it doesn't apply to ALL computers:
https://www.asus.com/us/support/FAQ/1034920/

Still confused.  Bitlocker gets enabled by default with Office 365.  I have never heard of suspending bitlocker, and I update the BIOS on machines every day without issue.  We do not have any ASUS computers.  Is this recommended procedure?  I did read "Doesn't apply to all computers", but asking yours or MS opinion on this.

Do you mean *MICROSOFT* 365?  Office 365 has nothing to do with BitLocker.  BitLocker is a WINDOWS feature.  Has been for years.  It's not an ASUS feature - the ASUS article was posted in support of my previous statement that this was likely due to a BIOS update done without suspending BitLocker.

MS Office 365.  When you install that, it enables bitlocker (Part of the Windows OS).  

I see your Windows feature comment.  I think we are saying the same thing.

Office, Excel, PowerPoint, etc. are Microsoft Office Products.  I have installed Office and Office 365 on clients for 20+ years and Bitlocker is not a feature of Office.   I'm perplexed why you keep pointing to Office. Most people have Microsoft office installed. Again, Microsoft Office has NOTHING to do with Bitlocker.  BitLocker is a feature of *WINDOWS*.

I've explained why this frequently happens (could it be something else, sure; bottom line, you need to turn off bitlocker, unencrypting the drive, then (optionally but STRONGLY recommended) re-enable it).  Then you should NOT perform hardware changes (which a BIOS/Firmware update) would be considered - without first suspending bitlocker.

You are correct, bitlocker has nothing to do with Office software.  That is also what I am saying.  When you install Office 365 (Now called Microsoft 365), it will enable bitlocker.  You can also do this manually.  We could choose to disable bitlocker after the Office install, but we have no reason to do so.  Office 365 keeps the bitlocker information in the cloud, so loosing the information is not a problem.  I am not sure why you are stuck on Office and bitlocker being one product, as that is in no way what I am communicating.  The relationship is only the fact that it enables bitlocker.  
I have 24 years experience in IT doing this very work.  To confirm >>>  BITLOCKER is a feature of Windows.  

Microsoft in their infinite wisdom has made this confusion common. i.e. Office 365 has several SKU's some of which have desktop AND cloud, some are only cloud, some have exchange, some do not..
Microsoft 365 can include the OS AND/OR the Office 365 SKU's
Now one has to for claritys sake when referring to Microsoft 365 state the exact SKU

I've seen later papes that separate it out
Microsoft 365 - OS and Desktop APPS
Office 365 - no OS

When you install the OS component it implements bitlocker.

Can you expand on the part about the OS component implements bitlocker.

OS  component is the operating system Windows 10

I meant expand on your thought.  I think everyone is saying the same thing, but differently.  So far, I haven't learned anything I didn't already know.

Although no BIOS update was performed, disabling the bitlocker and re-enabling it was the solution.