I'm not sure if I wasn't clear but your information is not correct.
First, yes, you can deduct expenses on Schedule C even if you do not show a positive income. It will be reported on your 1040 as a NOL which can offset other sources of income or act as a carry forward NOL if you have no income. You can also carry back a NOL 5 years with the Tax cuts and Jobs act of 2017.
Regarding the day trader losing money - of course you shouldn't be losing money, however most do. If however you are net positive, Turbo tax still poses a problem which was my entire point:
A mark-to-market trader will report the following:
Gains are reported on 4797 Part II
Expenses are reported on Sch C
Schedule C will show $0 net income (because all gains (or losses) are reported on 4797) which Turbotax prevents you from deducting the home office deduction because the IRS does not allow you to deduct for home office if you have no income from the business, even though all your income is reported on 4797 instead.
This is a limitation (flaw) of Turbotax that is allowed by the IRS for Day Traders who are TTS.
