Breaking up standard oil famously created a lot more value.

Apparently that's still controversial (I learned just now while trying to learn more about the breakup). However, it was easy to see cut lines in Standard Oil.

Breaking up (and privatising) the UK national rail network didn't work so well; a few years after it happened, the party who did it lost power, and had apparently forgotten they had even done this to the trains as they were running ads saying "you paid the taxes so where are the trains".

Apple's iPhone can clearly be split into "hardware" and "software" because Android QED; but that's not sufficient because the Play Store gets much the same criticism.

Likewise the App Store can obviously be split off, the technical issues are demonstrated by what already exists. But, the Samsung store isn't stopping the criticism of the Play Store, so alt stores are also not enough here for iOS either.

I was expecting anti-trust issues before it reached "just" one trillion dollars of market cap, let alone three, so who knows.

There is such a thing as a natural monopoly. Usually these are more efficient when run by the government because they inherently cannot benefit from the advantages of market competition.

My guess is that, whenever there's a possibility of innovation then competition is great and private corporations are the best; but when that period comes to an end, when the private corporations naturally merge together to save money by eliminate duplicate functions or improving scale efficiencies, then government buy-outs, nationalisation, is the best — everything that would have been a shareholder dividend, instead becomes a taxpayer saving.

Even if this is correct (unlikely, I'm not an economist) I have no idea how it would interact with globalisation/multinationals.

I'm not sure what amounts to "personal computing" is quite a natural monopoly, but it is important and foundational enough for modern life that it deserves special protection.

Personal computing is not quite a natural monopoly because it's easy to buy a different device but the rent seeking app store and not letting users install their own software is absolutely an anti competitive monopoly.