Subject: Re: Adjusting BRK-centred retirement portfolio
... Berkshire's AAPL holding has increased to about 22% of Berkshire's total market value...

This is a rather slippery concept.

The market cap of the Apple shares that Berkshire holds is presumably around 22% of the market cap of Berkshire. I trust your arithmetic.
But is that a meaningful metric?

The Apple holding is a substantially lower percentage of the value of a share of Berkshire, which is in the mid-high teens.
Simple proof: do the same exercise for everything Berkshire owns, and you'll get something far more than Berkshire's market cap.
Quite aside that markets are stupid enough not to be able to add, Berkshire also has a lot of liabilities.
It's also not 22% of Berkshire's assets, nor 22% of Berkshire's working assets.

The ~22% figure is a meaningful number only if you think Apple stock might be a "zero", in which case yes, that's the maximum potential hit to a share of Berkshire.

I see it this way:
* If the CCP decides Apple is to be tossed out of the country and made an example of--no sales, no manufacturing--that might hit the Apple share value by half.
(it would be utter chaos for a couple of years in Cupertino, but they would survive. The balance sheet is not flimsy)
* This might be a hit of ~10% to the value of a share of Berkshire. Pretty horrible, but very far from fatal.
For a sense of scale, in isolation that would constitute around a typical year of value generation.

The bigger issue would be the hit to the value (not just price) of almost all shares globally in the situation that would lead to this kind of problem at Apple.
Ferengi rule of Acquisition #35: Peace is good for business.
In that sense, it's a risk to all firms, whether they own Apple shares or not. More for firms that own Apple, but the problem is not limited there.

That's why I don't shrink my Berkshire position because of the huge Apple/China exposure: I appreciate the risk hugely, but I estimate that I can live with the worst case scenario.
Or, as mentioned, the portion of the worst case scenario resulting from the large size of Berkshire's position in Apple.
If Apple takes the hit because of (say) a shooting war in Taiwan, the Apple exposure is not going to be the decisive issue.

Jim