Hi Adrian,
Hope you are keeping well.
The notifications are managed by the end user, as the notifications are specific to each account.
The end user can also control which notifications they receive via the "My Preferences > Notifications area.
So in this case, they cannot be bulk deleted globally in this case, we have found that a lot of end users rely on Notifications to access certain elements of Frog, such as an assignment for example, so putting the notifications at an end user level helps with the user experience in Frog.
We have a tutorial here that should provide end users with the knowledge of how notifications work in Frog:
https://www.frogeducation.com/community/training/widgetguides/n-q/notifications
I hope this helps for now but if you have any further questions about this, please do let me know.
Kindest regards,
Tom