It is a business and you do have customers! Someone has to buy the stocks you sell which they are the customer and you can buy the stocks they are selling which you are the customer.
Everyone depends on that something and that something depends on everyone or it will not exist. If not for...
I registered as a single-member llc and classified as a disregarded entity for tax purposes and should have QBI losses for at least three years which I would then use to increase my capital for trading.I too trade part time until I retire and do not need my trading income.