I get plenty of antivirus 'your payment has failed, click to update' attempts in my spam folder, but to see a paid ad hosted on the free version of Outlook for Windows 11 is very troubling. I have Gmail connected to the Outlook app and this is where the ad showed.
https://imgur.com/a/O9bjjQQ
Edit: better screencap https://imgur.com/a/Qra5Ohp
Update: had to refresh a few times but it came back and here's where the 'ad' leads to: https://imgur.com/a/MSDzFhs