If your spouse had no reportable/taxable income in 2018, then they don't have any "their part" of the return to get back. So filing injured spouse would be a waste of time. You still file MFJ to keep your tax liability low, and will just have to accept the fact that if all of your refund is necessary to pay the debt, then all of your refund will be applied to that debt.
Now you can file injured spouse if you want. But you're wasting your time if your spouse did not have any income of their own to report for 2018.
