Hi @Lynn,
I have confirmed that reminders are turned on through the Office 365 settings and the site page has been given permission to display notifications.
Before we go on, could you clarify which kind of notification doesn't work? In-app notification which usually shows up in the upper right corner of the Outlook on the Web page? Or you are referring to the desktop notification?
Supposing you meant the desktop notification, from your description above, the following settings have been enabled via Outlook on the Web (https://outlook.office.com/mail/options/general/notifications), right?
With the above confirmed, it's also suggested to follow the other troubleshooting steps in the document below, double checking the configuration in both the browser and the Window Action Center:
Note: as mentioned in the link above, desktop notifications only works if your browser is running and OWA is either out of focus or closed. You won't receive desktop notifications when OWA is in focus, instead you'll receive in-app notifications.
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