A guy on YouTube made a good point that Apple PE ratio has expanded from from 20 to 33 despite declining revenue and earnings, [n]ot normal or sustainable and definitely bubble territory.

Expensive, yes, but I don't know about bubble territory. Revenue is slightly down, but earnings have held steady, within 5%. Apple continues to expand its user base, and an increasing proportion of revenues and earnings is coming from services, which are dependent on the number of users, with revenues from iPhones down close to 50% (it used to be more than 2/3).

I wouldn't buy it at this price, but Buffett has showed us over and over that holding on to a moderately expensive stock probably makes more sense than selling it every time it gets a bit pricey and hoping you will be able to get back in at a lower price (and you need a substantially lower price, when you factor in taxes on the realized capital gain you made.

That said, I think the risks are substantial, and represent by far the highest risk of owning Berkshire, with the Apple position representing 25% of Berkshire's market cap. Production in China is the obvious risk, sales in China is another important risk, and technological obsolescence is a non-trivial risk too. I know a lot of people here have big stakes in Berkshire, sometimes 40% and more, and if I were in that position, I would seriously consider hedging a big part of that Apple exposure. For those who can't stomach the idea of selling shares short or maintaining a semi-permanent position in puts (at, say, $100/share), another option might be to own shares in Apple's major phone OS competitor, the one with no exposure to China, the one that sends about $20b to Apple every year, almost a fifth of Apple's operating earnings.

dtb