How to replace the old "Awake"?

The old Awake was called when the script was loaded even if the the gameobject was disabled.
The new Awake was called only when the gameobejct is active.

How to replace the old Awake() void with something else?
I have to run a command at the start, on inactive gameobjects.

(the pages in my game menu are inactive at the start, but they have to find their components at the start.
Other scripts can refer to the menu pages, even if they are inactive, so I have to run that command before the gameobject is enabled)

Awake was never called on disabled gameobjects. It is called in disabled scripts if the gameobject is active. However there is no initialization callback if the gameobject is inactive. There never was one.

So you want to rely on scripts that conceptionally do not participate on the game to do something for you. This is simply the wrong approach. If they need to be inactive, you have to trigger any initialization from outside. Either use lazy initialization, or provide your own initialization method that you call from another script.