It depends on the customer. Apple and Nvidia indeed license just the ISA and build their own CPU implementation from scratch. At the other extreme, you can make

It depends on the customer. Apple and Nvidia indeed license just the ISA and build their own CPU implementation from scratch. At the other extreme, you can make a complete chip just from ARM IP - they have way more than CPU and GPU IP, they can sell you pretty much everything else, too. At the middle are chip makers taking eg ARM CPU IP but no other ARM IP and making other IP themselves or licensing from other vendors.