You deduct ordinary and necessary business expenses on schedule C. If the business is not active in 2021, you don't have a schedule C and can't deduct startup costs. You will deal with your startup costs on your first tax return after the business is active and reports gross income. Very briefly, you can take up to $5000 of startup costs as a deduction. If your startup costs are more than $5000, you may deduct some as an expense and must amortize the rest over 15 years, according to a formula.
Since you won't have a schedule C this year, you have some time to educate yourself.
https://www.irs.gov/newsroom/heres-how-businesses-can-deduct-startup-costs-from-their-federal-taxes
https://www.irs.gov/publications/p535
https://www.irs.gov/publications/p583
