Revision : The present perfect
1. Experiences and finished actions WITHOUT a specific time.
2. Unfinished actions.

The superlative can be used with the present perfect to talk about experiences and unfinished actions.

e.g.
superlative +noun + that I have ever + preterit

EXAMPLES:
This is the best film that I have ever seen
It’s the best coffee that I have ever drank !
It was the most boring movie that he’s ever made !

CAREFUL!
In these sentences « that » is optional.

It’s the most underwhelming performance that he has ever given ! ⇒  CORRECT
It’s the most underwhelming performance he has ever given !  ⇒  CORRECT