Glad you are asking abut DropBox. I don't know how that works but a lot of people are losing their .tax files and finding them there. How are you opening your tax return? Can you find your tax file on the C: drive in Documents? Try double clicking on the actual .tax2024 file in Documents. Maybe you think you are opening it from your computer but it is a Document folder under DropBox?
I would try moving the tax files from Dropbox to your local hard drive. Should be in your Documents in a TurboTax folder. And when you are done and exit don't do a File-Save. Do File-Save As to tell it where to save it.