My spouse's employer withheld state tax for OHIO but we live in TX. He's never worked in Ohio. How can I file our joint tax return on TurboTax?

Yes you will have to fil a nonresident Ohio tax return.  On the Ohio return where asked for the Ohio income make sure you enter $0.

In the My Info section of the program you are asked for your resident state so you should have selected Texas.  Further on you are asked if you made money in any other states, answer Yes and choose Ohio as the state.

After completing the federal tax return section you will then be able to complete a nonresident Ohio state tax return and get a refund for all the Ohio state income tax paid.

Make sure your employer is no longer withholding OH state taxes from your wages for 2025.