You think that the Easter eggs in the ship diagram in Engineering is just for fun, no. It’s actually canonical to the series.
How is an automobile, a prop plane, a rubber duck, and giant Dremel canon? Remember what the Enterprise-D is to Starfleet. It was the biggest, most luxurious starship ever built. It was designed to have a large population of civilians. Remember the first episode of TNG? That display in Engineering is not privileged access, there were families with children consulting the display to find things on the ship. Engineering is a critical area, but it’s not classified. Starfleet wanted civilians to visit and see the crew in action.
In addition to being a Carnival Cruise liner, it’s the Enteprise! The flag ship on a permanent first contact mission. They wanted attractions onboard for the residents and visitors to enjoy. There’s an old Earth automobile on display, there’s an old Earth airplane on display. The drill is clip art of a drill, but what if it was meant to represent an old Saturn rocket? It makes sense that Enterprise would have a small museum onboard in addition to other attractions like the arboretum and holodecks.
So… why a duck? Because there’s someone else living on the Enterprise. A certain aquatic species of Earth that turned out to be far smarter than they were originally given credit for. The duck was their idea. They insisted. They just really like rubber ducks. So a giant one was installed on the Enterprise at their request.
Bonus fanon: They really do decorate it for Christmas. They just forgot to take the decorations down and Data got confused.