I subscribed to this feed: https://support.microsoft.com/en-us/feed/atom/029dceb2-58a4-5a51-90fe-a66b7669017d

I had like 900 notifications, I make everything as read.

A few minutes later, 1200 notifications. I mark everything as read.

A few minutes later 1500 notifications, I make everything as read.

A few minutes later 1900 notifications, etc...

I have the latest beta on both macOS and iOS.

Not sure if it's a beta bug, a sync bug or a feed bug.