I Looked the below Microsoft site then I found that saved in cloud office file the AutoSave can be turned off.
The default for AutoSave is to always be On for files that are on the cloud. However, if you turn AutoSave Off for a file, the program will remember and will keep it off every time you reopen that file.
But I tested in my tenant I cant found how to disable AutoSave. If there is a way can disable the AutoSave function please tell me the method.
If the above site's information is wrong please tell me.