I dont recall if it was Apple that did this, but theres trick one can pull with an "open source"codebase thats part of a proprietary product.

One can have said codebase effectively outsource functionality to function calls on closed source libraries.

Google does something similar with android except in that case its moreso coupling functionality to their services:

https://arstechnica.com/gadgets/2018/07/googles-iron-grip-on...