Allow Patrons to Request Items in Work Orders
Currently, all work orders automatically make all items in that work order unavailable to patrons in the catalog. Some work orders may be for workflows or processes that can allow for items to be requested and pulled for users.
If, during the setup and configuration, work orders have the option of "allowing patron requests" or "do not allow patron requests" (similarly to how recall notices are an option), then some work orders can allow for patrons to request items so they can be pulled and delivered, based on the work order type.

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Stacey van Groll commented
The current behaviour is to allow patrons to request items in work orders, and by the title this is already supported.
But from the text of the submission, it's really the opposite ask - to add a configuration option to configure specific work orders so that it's not possible to place a request when an item is in that particular work order. -
Are items in work order processing not requestable for you in Primo ? That may be a configuration issue.