In Pro 22 when saving a project, I can't go back in and make changes like in previous versions. Pro 22 saves as completed. Unless I don't know or am saving wrong.
Keep multiple project files. Legacy project files will open in upgraded versions of Vegas.. but not the other way around. Timeline events can be copy/pasted though.
maybe the file has become write only somehow? click it's properties and see what the permissions are.
@james-t First of all, "Sony Vegas Pro 22" not exists. See: https://www.vegascreativesoftware.info/us/forum/sony-vegas-vs-vegas--119881/
As for your question, I think your words are not very clear, but I believe you "opened" your project in the wrong way? This will make the timeline appear as a single completed video event.
One mistake beginners often make is to directly drag and drop a veg project file into the Vegas timeline. This actually imports the project file as a nested project rather than opening it as they might expect. However, in the newer versions of the Vegas File Manager, double-clicking is also treated as importing a nested project instead of opening the project. (I never use it btw, so I don't know if this issue has been fixed.) For project files, you can right-drag it to the timeline, then select "Open Project File" to open the project in the current instance. You can also open project files through "File -> Open".
If your question is not what I think, you'd better take a screenshot, which will help us understand.