Outdoor lamp installation without outlet box
Weather metal or plastic there looks to be a box in this location. Removing the old screws and putting the new ones to hold the fixture will be fine, I believe it is not metal because I can see a 3rd wire not connected to anything a metal box would require the box to be bonded. Pull the old screws put up the new fixture, if metal used the bare copper to the new fixture bare copper if plastic just connect the black and white to the new fixtures black and white.