You cannot file two years together. You have to file a separate tax return for each year. You can use TurboTax to file for 2023, but not TurboTax Online. TurboTax Online is only for the current tax year, which is now 2024. To file for 2023 you have to use the desktop TurboTax software for 2023. You can purchase a download at the following link.
Past Years' Products
The desktop TurboTax software can only be used on a Windows or Mac computer, not on a mobile device or a Chromebook.
Tax returns for past years cannot be e-filed. You will have to print your 2023 tax return, sign it, and file it by mail. When you file by mail you have to attach copies of your W-2s and any W-2G or 1099-R that has tax withheld. We suggest that you mail it by certified mail with a return receipt so that you get tracking and confirmation of delivery. Mail your federal and state tax returns in separate envelopes, because they go to different places. Follow the filing instructions that TurboTax prints.