Thanks for chiming in on this thread, Spooners.

To verify, are you trying to reactivate a job? If so, the checkbox option will be grayed out if the main customer is also inactive.

As to what my colleague MadelynC mentioned above, you will need to reactivate the customer first. Then, the Job is inactive checkbox will be available. Here's a sample screenshot of the before and after reactivating the customer:

To help manage your jobs in QuickBooks Desktop, you can read this article: Tracking job costs in QuickBooks Desktop.

In case you need help with other task in QuickBooks Desktop, you can visit our general help topics page. Just type your concern in the search field and this page will route you to the related help articles, Community discussions, video tutorials and more.

Please keep me posted on how it goes on your end. I'd like to make sure this is resolved for you. Take care and stay safe.