You could do this a variety of ways. Ball mill would work fine.

If you were doing this in "real" volume, you would likely likely just cast aluminum into this shape.

However, companies like apple/amazon/etc have a tendency to just find a supplier who can sell them semi-specialized machines and buy a lot of them.

Apple has bought out (either the machines or capacity) for things like laser drilling.

Amazon echo/echo show's were made by buying a ton of semi-custom machines from these folks: https://mdaprecision.com/

(They talk about it in various places)