Having trouble enabling Apple's iCloud Advanced Data Protection? Is it that you keep getting inexplicable errors or silent fails when you try? I've done some troubleshooting and found several distinct errors and their fixes, and blogged about it here: https://www.tarah.org/2023/01/27/troubleshooting-apples-icloud-advanced-data-protection/
Also, fully activate ADP before trying to add security keys! I've had a lot of issues and had to troubleshoot for 2 days with my iPhone after 16.3 was released.