I "earned" money in December 2022, but was actually paid in January 2023. Does that count as 2022 or 2023 income?

Do you get a W2 or 1099NEC for your pay?   It will go on 2023 next year unless it's included on the 2022 W2 or 1099NEC.  Depends on how the employer reports it.

A very very few independent contractors might operate on the "accrual" accounting basis, which means you book revenue when earned rather than paid.  This is complicated and usually requires an accountant to set up, you would know if you used this system.

Everyone else, whether self-employed or a W-2 employee, is considered a "cash basis" taxpayer and you report income when it is actually received and expenses when you actually pay them, regardless of when the work was performed. 

if you were paid in 2023, it should be 2023 income.