Can the Xiaomi MIX Flip set a lock screen password for the external screen?

The Xiaomi MIX Flip's external screen does not have a separate lock screen password setting. You can set the lock screen password through [Settings] >> [Fingerprints, face data, and screen lock]. This password is shared between the internal and external screens, meaning both screens use the same password configuration. However, you can unlock the device from either screen individually, providing flexibility in accessing your phone whether it's folded or unfolded.

Does it help?

Yes