Excel Keeps Showing Me Special Offers

How do permanently turn off these ads? These are popping up multiple times a day:

"LIMITED TIME OFFER For just AU$$1, get 3 months of Microsoft 365 Family with up to 6TB cloud storage (1TB per person) plus premium Office apps. TERMS APPLY."

I have closed the banner in the app using the "x" on the RHS, however it keeps reappearing.

If there is no setting, does anyone know whether a key could be modified in the registry?