Delete Nofications List?

General
1

When I click the Avatar icon (‘no’ red dot displayed), a list of ‘already-viewed’ Notifications is visible.

How do I delete/clear the list, either one at a time (or together) ‘or’ does each one ‘self-delete’ over a preset amount of time ‘or’ is there no way to delete/clear them at all?

2

I had no idea that my question would be so complicated to answer.