Samsung has finally figured out how to lock the screen

[Sherlock221B]

Yay, finally the most awaited feature is here. Received UI 3 upgrade on A51 and with a massive addition of a feature... guess what? 

Hah, Lock your screen without a lock key! 

[Shahinmarzia]

Good 👍

[souravKhan]

Actually you are very late to come to know this because this feature came in A51 with One Ui 3.0 update on 17th Feb.