The relevant thing here isn't the chips, it's tying things to the chips, because those would otherwise be separate markets. If you could feasibly buy an iPhone and install Android or Lineage OS on it or use Google Play or F-Droid on iOS then no one would be saying that Apple has a monopoly on operating systems or app stores for iOS since there would actually be alternatives to theirs.
The fake alternative is that you could use a different store by buying a different phone, but this is like saying that if Toyota is the only one who can change the brake pads on a Toyota and Ford is the only one who can change the brake pads on a Ford then there is competition for "brake pads" because when your Toyota needs new brake pads you can just buy a Ford vehicle. It's obvious why this is different than anyone being able to buy third party brake pads for your Toyota from Autozone, right?
> It’s also probably relevant that MS was not selling PCs or their own hardware.
This is the thing that unambiguously should never be relevant. It can't be a real thing that you can avoid being a monopoly by owning more of the supply chain. It's like saying that Microsoft could have avoided being a monopoly by buying Intel and AMD, or buying one of them and then exterminating the other by refusing to put Windows on it. That's a preposterous perverse incentive.
Move the most important aspects of your software to hardware. Hard for MacOS but for a Chromebook style thing you could write the browser into its own pice of wafer.
Google should pay me to be this evil.
So now you have a piece of silicon with a two year old version of Chrome with seventeen CVEs hard-coded into it, and still have all the same antitrust problems because the device still also has an ordinary general purpose CPU that you're still anti-competitively impeding people from using to run Firefox or Ladybird.