Personal property you sell at a loss is not deductible, it's just life. The loss on your GPUs is the same as your loss on a used car, used sofa, or dropping off your old clothes at Goodwill.
A loss on business property is deductible against business income, but you would have to declare your CC mining as a business, which would totally change your last few years of tax returns. And, depending on how you entered the equipment as a business asset, you might actually have a taxable gain when you sold them.
We can discuss this further if you want to re-do all your taxes for business activity.
