What does iCloud Keychain sync?

I don't think iCloud Keychain syncs server passwords - at least it doesn't for me. Other passwords that you can add to Keychain outside of Safari, for example usernames and passwords for Screen Sharing, are stored in the local Login and System Keychains rather than iCloud Keychain (again, at least for me using default settings, maybe it is possible to force it to store in iCloud Keychain).

iCloud Keychain stores and syncs:

• Safari usernames and passwords
• Credit cards (excluding security codes)
• Wi-Fi network information
• Internet accounts (such as accounts in Mail, and also system-level Facebook and Twitter accounts, etc.)

https://support.apple.com/en-gb/HT204085

(I'm sure from a technical perspective the Keychain element of iCloud is responsible for encrypting and syncing a host of technical data, but those are the only user-facing items it syncs AFAIK.)