This works for me! I just have one comment about a cppcheck error.
Also, it would be interesting to write a test for this if you're interested, but it's not required. The test would go into MainWindow_TEST, trigger save / save as, fill the browse dialog as needed, verify that the file was created, then delete the file. There is a similar example here; it's not exactly the same because save and save as have slightly different meanings there, but the way the action is triggered and the file is saved should be the same.
Actually yes @Louise Poubel ! The method of triggering the menu is varied here. Instead of Ctrl+Shift+S or simply clicking the option in the menu one uses Ctrl+S to trigger SaveAs. How does one incorporate the method of a trigger in the test?
EDIT: Actually I think I got this. But as I have modified the Save function in this PR, wouldn't it be better to just modify the Save Test than to create another one for this?