in some case user may need more windows for data and working area so the Ribbon menu can be minimized and maximized when you want to.
The problem you may have found is that more than one person using one PC or Laptop and someone who may be more computer skill and knowledge may minimize the Ribbon menu for his job to be done and might forgot to bring it back.
Later on ,when you come to use the same software and then you could not find the Ribbon menu as normal to finish your work.
two way for solution
Solution 1The Ribbon tab Ms Excel 365 can be minimized and maximized base on the users need.
How to do this is very simple and quick.
1 Open up the program.
2 On the Ribbon menu go to Home tab
3 Double click on the Home Tab to minimize and maximize.