I am making a game that will have multiple monsters. I want to set up some sort of system that is akin to inheritance, however I have never set something up like that in a game engine. For example, I want to have a base scene or something called entity, that will have everything that all monsters and npcs will have. then I can create new scenes that inherit from entity to streamline the process, and avoid repeating stuff. How would I accomplish this in Godot 4, if something like that is viable.

I think you are talking about something like this, but there are lots of tutorials on youtube, just do a search for godot4 classes.

This may be helpful:

Imagine we started by creating the room. We could make a couple of different room scenes, with unique arrangements of furniture in them. Later, we could make a house scene that uses multiple room instances for the interior. We would create a citadel out of many instanced houses and a large terrain on which we would place the citadel. Each of these would be a scene instancing one or more sub-scenes.

https://docs.godotengine.org/en/4.1/getting_started/step_by_step/instancing.html#scene-instances-as-a-design-language

Read the upper part of that page for a specific example.