"For additional privacy and security, 15 data categories — including Health and passwords in iCloud Keychain — are end-to-end encrypted. Apple doesn't have the encryption keys for these categories, and we can't help you recover this data if you lose access to your account. The table below includes a list of data categories that are always protected by end-to-end encryption."

The FileVault keys are stored in the iCloud Keychain and Apple does not have access to them, full stop :-)

Nah, the FileVault key is stored in your iCloud Keychain when you choose to backup the key to iCloud. And the keychain is end-to-end encrypted. Only the user has access.

In Apple's case, even when the user enables iCloud FileVault key backup, that key is still end-to-end encrypted and Apple cannot access it. As a matter of fact, while Apple regularly receives legal warrants for access, they are ineffective because Apple has no way to fulfill that request/requirement.

Microsoft has chosen to store the BitLocker key backups in a manner that maintains their (Microsoft's) access. But, this is a choice Microsoft has made its not an intrinsic requirement of a key escrow system. And in the end, it enables law enforcement to compel them to turn over these keys when a judge issues a warrant.

If the user's MacOS FileVault disk encryption key is "stored in iCloud" it resides in the users iCloud Keychain which is end-to-end encrypted. This creates a situation similar to the iPhone, where Apple does not have the ability to access the user's data and therefore cannot comply with a warrant for access (which really annoys organizations like the FBI and Interpol)