I am trying to create a custom field that allows me to choose an entire year (FY2023 etc..) but when I choose the accounting period list type it only allows me to choose individual months. Any ideas?

I think the quarter and year are just fields on the base period itself, not records/lists in and of themselves. Depends upon your use case, but you could just report out the year from the period selection, or you could create a custom list with just the years.