I dont think you can stop the autosave but if you can turn off the version settings from the document library but i dont think this is what you want.
MSFT turned on this feature due to putting extra layer for recovery.
You may select minor version settings from Document library.
Behind the scenes, once a file is saved to a SharePoint Online or
OneDrive for Business site, AutoSave silently creates new versions of
the file in the document library to capture changes made by the user.
Depending on the versioning setting for the library, AutoSave creates
a new major or minor version of the file.
Not every change results in the creation of a new version. Instead,
AutoSave uses a version for between ten and fifteen minutes before it
generates a new version and switches to it to continue saving.
Read more here: AutoSave: Nice Feature, but Office 365 Tenants Need to Keep an Eye on Network Demand