This is obviously not tax advice, but I think the earlier poster is referring to reductions to AGI that are on "schedule C" titled "profit or loss from business". Some tax language seems to refer to these as "deductions", but they are distinct from the "itemized" or "standard" deduction. Schedule C goes to Schedule 1 goes to 1040 line 7a. The standard or itemized deduction is on line 9. The Qualified Business Income Deduction on line 10 is another AGI-reducing gimme for people who get 1099-income distinct from the standard or itemized deduction. And don't forget, your eligibility for Marketplace plans including subsidies is based on your (Modified)AGI, not your gross income, which can be a costly mistake (Based on what I understand now, in 2020 my household would have been able to get a marketplace plan with subsidy but we didn't due to not understanding the income guidelines).

(note: I may have mixed referring to 2019 and 2020 tax forms here, particularly wher I cited line numbers)

Not tax advice, iana accountant, etc.

I think in canada (where i live), you can just deduct all the business expenses (things that are part personal like rent have to be the reasonable porportion related to the business). You can't deduct more than the income from the business in a year, but you can carry over your expenses to the next year if you have more expenses than income.