That is part of the entire problem in the industry. No standards and no accountability. Those with the purse strings only invest in security that is marketable or protects IP. Anyone that invested in proper remotely attestable provably quorum managed systems is going to be bragging about it and happy to show off the proof to earn trust from their customers. I do.
When no one is bragging about doing these things, it is because they are not doing them, and they just have a bunch of humans running around with god powers to execute any code they want on production systems or in binaries that will end up on your laptop.
To get a clue about their internal practices, lets see what they do when everyone is watching in public.
https://github.com/apple/foundationdb/commits/main/
No signed commits, no signed reviews. Merges done via browser. One Github API token away from being supply chain attacked. Also put one of those recent usernames into "forgot my password" and you can verify they do not mandate hardware 2FA. One compromised email account and you get to make a PR as a rando, then merge it with an Apple account and huzzah, you now have code in a critical repo used internally at Apple. Also releases are not signed or reproducible and are just cut by github actions. Another API key you could use to be even sneakier.
Almost any community maintained Linux distro does way better than this. Inexcusable for an org of their resources.
If this is how poorly Apple handles supply chain integrity in public, why would anyone believe they do any of this internally. I have also talked with multiple current and former Apple employees close to such things off the record but obviously will not out which ones.