I just want to point that new Outlook app for Windows 11 is really just a website opened in app through Edge WebView. Because of this, it can serve you ads and you can't block them. Instead, I'd advise anyone to just stick with Outlook.com webmail and to enable browser notifications. It's practically the same, you keep ability to use your favorite ad blocker and you don't have to add Microsoft account into Windows to use it. Just make sure to enable browser notifications and that's it! You'll get notified about new mail as long as the web browser of your choice is opened, even if you don't have Outlook.com opened in any browser tab. You can also set this up with other e-mail services that have browser notifications support.
I recently switched to Firefox and struggled to make notifications work. It appears that Microsoft "reorganized" notification settings menu and now it's required a bit more steps to enable them. Once I did it, they started working right away. So, to enable browser notifications, you have to expand e-mail category and select browser notifications. And when browser asks you for permissions to show you notifications, just accept and save the settings on Outlook's website.