Configuring preferences and options in Outlook.com
Hi my name is Adam I'm an independent adviser, I would like to help you with your question today,
Ads have been on outlook.com free email accounts for quite sometime. Unless you subscribe to premium features, or office 365 for an ad free experience.
A possible reason for ads not appearing before is if you were using an ad blocker on your browser before that is now turned off.
There is no setting to turn this off unless you pay for the premium experience. https://premium.outlook.com/?sl=1#/OfferV3
https://support.office.com/en-us/article/premiu...
I Hope this answers your question