Re: diversification: keep in mind, your income is already dependent on the company. So, if bad news came, then it could affect your income *and* your net worth. If you are a company insider, meaning your trades are legally limited because of your non-public knowledge about the company's performance and strategy, then yes you might ignore regular diversification and use your particular knowledge advantage over the market. If you are a worker drone, and do not have Tim Cook's cell number, know the rollout date for the Apple Car, or direct the sourcing strategy for semiconductors, then you are right to be concerned.
And even as a company insider, you have no control of other things, like if China decides to get more aggressive toward Taiwan, or makes a further data restriction on foreign companies.
Traditional advice would be to have no more than 10% of your investments in any given choice, or 1/n, where n is the number of your holdings. (In individual stocks, for example) However, if you are indexing, keep in mind the high representation Apple already has in the S&P 500 and the NASDAQ QQQ. You probably already have a ton of Apple.
It is great to work for a company that is so successful. I am sure many of your colleagues are bragging about how well they are doing; as was mentioned, that was also the atmosphere at Enron. Things are good until they aren't. While I don't think Apple is Enron, at $3T valuation, I would say the Apple Car is already expected by the market. Should it again get cancelled / indefinitely delayed / reduced to a more-modest systems capability / supplier position, the stock could take a huge hit.