Let's start with the date the business begins as an active, ongoing enterprise. You are actively looking for clients, performing work, etc. even if you haven't been paid yet.
Anything before that is "startup costs."
If your business is active and ongoing before the end of 2023, then you file a schedule C to report your expenses. If you have no income, you will show a loss, that can be carried forward to offset profits in future years. Your costs before you started the business are startup costs. If they are $5000 or less, you can deduct them in the first year. If more than $5000, you deduct them partly in the first year and partly spread out over 15 years.
However, if you are not actively pursuing the business in 2023, then you hold onto your startup costs, and report them on schedule C in the first year the business is active (presumably 2024). You would not have a schedule C in 2023.
(I wrote this assuming it was a single member LLC disregarded entity. If this is a multi-member LLC or you made the election to be taxed as an S-corp, I don't know if the rules are different.)
Note that capital equipment is handled separately from other startup costs. Equipment is placed in service for depreciation as of the date the business is open/actively ongoing in the usual manner for equipment, including the options for the $2500 safe harbor, bonus depreciation and section 179 depreciation, if you are otherwise eligible. Other startup costs like legal fees, advertising, paperwork, building your web site, and so on, would be deducted or spread out over 15 years as mentioned.
