For example, it is new in Tahoe that they store your filevault encryption key in your icloud keychain without telling you.
https://sixcolors.com/post/2025/09/filevault-on-macos-tahoe-...
iCloud is much more secure than most people realize because most people don’t take the 30 minutes to learn how it is architected.
You can (and should) watch https://www.youtube.com/watch?v=BLGFriOKz6U&t=1993s for all the details about how iCloud is protected, but especially the time-linked section. :)