The program is not very functional until January and is continuously updated after that. The IRS won’t accept returns until late January.
If you are using the download version of 2024 TurboTax for planning purposes, I suggest making the entries in forms mode which does not prevent you from making entries in the sections that step-by-step mode does not yet support. However, there are likely numerous cost-of-living-adjusted values that have not yet been updated for 2024, so you may need to do overrides to get reasonably accurate results until TurboTax has been sufficiently updated. I would not yet begin preparing the actual tax return that you intend to file or later convert your planning-purposes file into your actual tax return for filing since it's all too easy to create erroneous entries in forms mode. Keep your planning file and actual tax return file separate.
@nmartens No they don’t notify you when it’s ready. They usually put out updates on Thursdays. So if your program doesn’t automatically update when you launch it then you can try getting the updates by going up to menu item Online - Check for Updates