This is happening because of the ngons. If you look your model from side, you'll notice the face is not actually flat.
There are two ways to fix them.
First(quick and dirty): use Weighted normal modifier with
Keep Sharp option enabled.
The shading is better now. However, the topology issue stays still since the
Weighted normal modifier changes normals only.
Second(better way to handle this issue): Recreate the model and use
Weighted normal modifier on it. There are unnecessary bevels(like the "triangle-shaped" bevels that will create the shading issues on your model. Moreover, they will create unnecessary vertices.
If you want diagonal face with bevels, the topology should look like this:
And because this topology still makes ngon on the top(which will make shading issue too), use
Weighted normal modifier to fix the shading issue.