I filed jointly for 2020. My spouse was self-employed at that time. Spouse did not end up working in 2021, so I paid in his estimated taxes to avoid a penalty. What now?

I want to get that money back since he did not work. How do we go about that? I am filing separately for 2021. Can I claim that I paid in estimated taxes? Or does he need to file to get that back, even though he had no income to file?