You need energy to produce a force that compensates gravity. So if you apply that force for a huge amount of time, will gravity ever be depleted?
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I think it’s important to clarify what energy is. You do NOT need energy to compensate gravity. A force diagram of the computer on your desk right now would show: gravity pointing down, and the “normal force” pointing up the exact same amount. The “normal force” seems like a weird force – how can it be exerting constant force without expending energy? For that matter, how can gravity or magnets do this too? It’s because force is VERY DIFFERENT than energy. Force gradients (like gravity from a planet) can exist in a steady state. Then objects can move up and down the gradient, and in so doing expend or release energy. But the gradient itself doesn’t require energy to maintain. The “normal” force I mentioned is actually simply the force exerted by objects that don’t want to be in the same place at the same time. Call it the Pauli exclusion principle if you want to sound fancy. But that tendency of nature to not let most things be in the same place at the same time is expressed as a force when you try to smoosh two things into the same place, like gravity.
So you’re left with gravity, a force gradient with no energy requirement, and the fact that your computer and desk can’t be in the same place at the same time (which can also be expressed as a force gradient, since they’ll push each other away harder if you try to smoosh them closer together), and they find their balance and there your computer sits.
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