Load custom scene BEFORE inspector scene is loaded?

I have a scene with all my Game Systems. These are systems I want to have active throughout the game.

What I want is specifically this: I would like it that when I enter playmode, the scene with the GameSystems is loaded BEFORE the hierarchy scene.

Is that possible?

 

Yes but scene loading requires one frame. You can make a singleton pattern that requires any singleton in your game to load a scene additively. But like I said you can't use it until next frame, so the singleton instance returned would possibly not yet be valid.

You can also make an editor script to always jump to your "zeroscene" first when you hit play. There's plenty of such handy scripts out there to look at.