So I am trying to make a backrooms game in Godot. How do I make the procedural generation for this kind of game?
You make one room, and have it as a scene. Instantiate the scene with a room index in your game scene. When you transition to a new room, regenerate the room. Now you have endless rooms.
In the single room scene, start making things different on instantiation. Like pick a random number of chairs, place them randomly in the room. Same with windows and doors and clocks and tables and enemies etc. Once that is working you can start working on different room scenes. Store the room settings against the room index so you can return to the same room.
Hope that helps. It is a bit of a general question.
Or try a tutorial (quick search revealed lots of these):
Can I use tutorials for procedural generation in a dungeon?
Yes you can use tutorials. Procedural generation is a pretty broad topic, but it boils down to using Random and Instantiating scenes, any one tutorial should fit for any other theme/assets.