Shopify doesn’t let you turn off those update emails, but you can get around this by making a new product every time you update the file. So, only new buyers will get the emails.
Or you can use apps like Sky Pilot or SendOwl, which give you more control over your digital files and notifications. you could host the files somewhere else (like Dropbox or Google Drive) and just share the updated link with your customers yourself. It is not perfect, but these ideas can help you avoid sending update emails to everyone every time you make a change.
Yup as Parampreet says you can’t turn this off via the Shopify app. If you need this functionality our app Alva Digital Downloads (with generous free plan) is a great alternative and will not update your customers when you update the file, unless you want it to!