Hello @Opus 17
tell me please if I buy bitcoin to sell and keep the fees as my profit. Can I write off that purchase, right?
I don't understand your question.
If you buy bitcoin, there is nothing deductible going on. If you sell it for more than you paid, your profit is considered a taxable capital gain, and is taxed as ordinary income (if held less than 1 year) or as a long term capital gain (if held more than 1 year). If you pay transaction fees to buy and sell, those are not "deductible" but they are treated as adding to the purchase price or reducing the sales price and they reduce your gain.
If you sell the bitcoin at a loss, the loss is probably not deductible as a capital loss, because losses on personal property are never deductible. To deduct a loss on bitcoin, you would have to be able to prove to the IRS you were acting as a professional investor.