Is miui SMS management enabled by default?

You are asking whether miui SMS synchronization management is enabled by default? Enabled by default.

Miui SMS management is enabled synchronously with the mobile phone. As long as the SMS function is enabled, the mobile phone will be synchronized and backed up to the mobile phone by default.

To turn it off, find the phone settings in the Miui phone, slide down in the settings to find "Sync", and turn off the "Turn on automatic synchronization" switch.