Does "Messages in iCloud" include SMS?

The page on Messages in iCloud mentions keeping "all your messages" on iCloud. It then goes on to activate the functionality on the iMessage settings tab in macOS.

• Does it apply to SMS messages?

• Does it only apply to SMS messages under certain conditions, e.g. only after enabling receiving SMS on another device?

Messages in iCloud applies to all SMS. The service can both be used to backup messages in iCloud and sync them across all your devices.

While it may be confusing to manage a SMS service setting under iMessage settings, it still applies to all your SMS if they have been synced from your iPhone. Mac cannot send or receive regular SMS themselves because they don't have the hardware required.