Sorry for all the confusion @MARK DERISLEY Earlier, I suggested that you work with your IT administrator to check the device more thoroughly, as we're only community/forum moderators and not Microsoft Support. However, you then mentioned that you're an individual user with no organization involved and that you're using Office Professional. And that's why I believe the Personal support team would be better equipped to assist you than I am.
You also mentioned that I should only reply if I have a solution. To be honest, I'm not sure whether my suggestions will completely resolve the issue or simply lead to more back-and-forth troubleshooting without getting you a satisfactory outcome.
However, if you're willing to try a few more things:
Method 1: Go to Word > File > Account > Account Privacy > Manage Settings, then disable Connected Experiences. After that, close all Office applications and reopen them to see if the prompt still appears.
If that doesn't help, try Method 2:
- Press Windows + R, type regedit, and press Enter.
- Navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\OneDrive
- If the OneDrive key does not exist, right-click Microsoft > New > Key and name it OneDrive.
- In the right pane, right-click and select New > DWORD (32-bit) Value.
- Name it:
KFMBlockOptIn
- Double-click it and set the value to: 1
- Restart the computer.
If neither of these options helps, and you are the only user and effectively the administrator of this Microsoft 365 tenant, I would recommend contacting Microsoft Support through the Microsoft 365 Admin Center for further investigation, as there may be something specific to your environment that cannot be diagnosed from the forum side. https://learn.microsoft.com/en-us/microsoft-365/admin/get-help-support?view=o365-worldwide
I hope this helps point you in the right direction. Thank you for your patience and understanding, and I apologize for any confusion caused.