Computer Configuration > Administrative Templates > Microsoft Edge
Both
HKLM\Software\Policies\Microsoft\Edge
Allows you to set whether users can view publicly accessible Office files on the web that aren't on OneDrive or SharePoint. (For example: Word documents, PowerPoint presentations, and Excel spreadsheets) If you enable or don't configure this policy, these files can be viewed in Microsoft Edge using Office Viewer instead of downloading the files. If you disable this policy, these files will be downloaded to be viewed.