Hi Fred,
I went through your post carefully and I spent some time on simulating some tests for your concern where it seems like the behavior you described are all by default since I can reproduce the exact same result when opening an online workbook from Excel desktop app. To make sure I can share with you clearer, I recorded two GIFs for you but due to the community upload limit, the quality might be low.
- First one, we can see this is an online workbook as the AutoSave is on, and there has a syncing status icon near the Save button on top bar. And only have Save a Copy on left File bar.
- Second one, it shows when I made some changes and I manually clicked the Save button, when I close the workbook and reopen it, the changes have been saved correctly. If you made lots of changes, you can monitor the Saving status finished as showing Saved before close the workbook for double safety.
As you can see, when I opened a OneDrive workbook, it indeed only shows the Save a Copy option on left bar. However, since the AutoSave feature is turned on for any OneDrive file, by default, user can edit as they want, and the changes will be automatically saved. So on the second GIF you can see, when I open the edited workbook again, the changes I made have been already saved. For some details, you may check this official article where it describes the details more clearly: What is AutoSave? - Microsoft Support
Hence, if I understand your concern correctly, I believe your demand is to make sure that the changes you made can be saved successfully to the original version of the workbook in case any possible data loss. If so, then I think you no need to worry about this and simply click on the Save button on top and close the workbook after the Saving process finished.
However, if the issue happening on your side is that the changes are not really get saved, then please come back to me and I will provide you some related suggestions regarding to the sync failure issue of AutoSave files. You may confirm by creating a new workbook saved to OneDrive and see if the changes can be saved/synced correctly like the test I made for you above, which will help to confirm if the issue is only happening on a specific file.
Please correct me if I made any misunderstanding or if there have anything else I can do for you.
Your patience is highly appreciated. Hope you a nice day and stay safe!
Best Regards,
Mia