Can business start up costs be deducted on '22 and '23 tax returns? I am in the process of starting up right now.

You don't file your first schedule C until you begin your business as an ongoing activity.  You don't need to be paid yet, but you need to be engaged in ongoing business activities.  (For example, if you are a graphic designer, you would be engaged in business activities when you begin to advertise your services and sign a contract, even if you don't get paid until a while later.)  Depending on what you are doing now as prep work, you might or might not be engaged in your business already.

Whenever your business is ongoing and active, you will file a schedule C with your tax return.  Startup expenses less than $5000 can be deducted as expenses in the first year of the business.  Expenses more than $5000 can be partly expenses right away and partly amortized over 15 years, according to a complicated formula.  Assets (generally, items with a useful life of more than one year costing more than $2500) are listed for depreciation using the usual methods when they are placed in service.