You should file your own tax return, as single (unless you have a child in your home, but you haven't mentioned any children). The joint return that your ex-husband filed is not valid, so you haven't actually filed a 2023 tax return yet. You will not be able to file your tax return electronically; you will have to file it by mail. It will probably take the IRS a long time to process your tax return, so be prepared to wait. Eventually you will get a notice from the IRS about the conflict between your tax return and the joint return that your ex-husband filed. Read the entire IRS notice carefully and follow the instructions in the notice for what to do. You might want to get help from a tax professional. Basically you will send the IRS a copy of your divorce decree showing that you were divorced before the end of 2023.
Your ex-husband will also get a notice from the IRS. They will deal with him separately. But that is not your concern, and it would be best for you to not get involved.
You might want to discuss the situation with your divorce lawyer, but be careful. Many divorce lawyers know a lot less about tax law than they think they do. Check any tax advice with a tax professional or a tax lawyer.
