Not all states use private prisons, and I don’t think all state prisons participate in forced labor (although they may all have ‘optional’ programs)

The optional ones probably vary from truly optional, to we say it’s optional but you’ll be reprimanded somehow if you don’t.

Edit: this random post says 3/4 are forced via threat

https://freedomnetworkusa.org/2023/08/11/forced-labor-in-prisons/