You need to complete The Pen and the Sword (Hantu Port) in Multiplayer.
Previously you could have completed this online with another player, but in 2021 there is nobody searching, I tried for an hour!
If you have a friend who also has Hitman 2 Hantu Port you can complete this with them. If not like me, I found a work around, however it needs x2 Playstation consoles to work.
With PS4 #1, make it so you are the primary user on the Playstation, this will allow other users on this PS4 to be able to play games that you digitally own, without purchasing them themselves.
Have your friend then sign into the PS4 #1, where they will be able to access Hitman 2 for free. On PS4 #2, sign in and because you have already purchased Hitman 2 for your account, and then simply invite each other into the Hantu Port level and complete it!