Can you sell digital products on Amazon?
Updated
Only through specific programmes
Only through specific programmes. There is no general "upload a file and sell it" option on Amazon. Ebooks go through Kindle Direct Publishing, apps through the Appstore, and music and audiobooks have their own routes. Templates, presets, spreadsheets and printables have no home there at all.
If your product fits a programme, the reach is hard to match anywhere else.
What does not fit
Templates, presets, spreadsheets, printables and most creative files have no home on Amazon.
Some sellers work around it by selling a low-content printed book, which is a different product with different economics.
What you get if you fit
Enormous buyer traffic and a trusted checkout. For an ebook, that reach is hard to match anywhere else.
In exchange Amazon takes a large share, sets the price rules, and owns the customer completely.
The usual answer
Use Amazon for the format it was built for, and sell everything else direct.
Many authors do exactly this: the book on Amazon for reach, the templates and bonuses on their own store.