Nubla

Story related, cannot be missed.

Once you have retrieved the paintbrush from the shelf, you will be back in the museum with it in your inventory. You'll need to go all the way to the left, past all the paintings you've been unlocking, where you will find the character waiting. Interact with the paper boat using and then press to pick it up when it's on the floor. You and the character will be sailing in the moonlight during the credits and the trophy will pop here.