Retention & Releases

I’m a subcontractor working on a large commercial project. We finished our work on the job in December 2020. We have been paid with the exception of retention. We provided a conditional final to request retention moneys. Our contractor is holding our retention until they complete their portion of the project. Each month they request unconditional progress releases in the amount of $0. Are we required to provide unconditional progress releases each month if we have already provided a conditional final? Also, how long can the general contractor hold our retention? The project over all was estimated to be completed in 2020, however, it keeps dragging on.