Can't switch on auto generate lighting

I’m following a tutorial and one of the early steps is to switch on auto generate lighting but on my computer this option is greyed out and clicking on it doesn’t do anything.

The player object was evenly lit so at first I just ignored this. But now I’ve reached the stage of implementing a game over function. When I restart the level by getting the scene manager to reload the scene, if this was triggered by the player falling off the platform the lighting on the player model gets a lot lower and it stays like this after all restarts. Triggering the reload by hitting an enemy on the platform doesn’t do this.

Can anyone suggest why auto generate lighting is disabled on my computer and how to enable it?

If I can’t do this can I stop the lighting changing after a scene reload?

I’m using Unity 2020.3.21f1 on Windows 10 Pro

In the new versions of unity, you first need to create a scene lighting settings object. At the very top of Window → Rendering → Lighting → Scene, there’s a button that says New lighting settings or smt. Press that, and now you can enable fog, enable auto generate lighting etc.