Comment 2 for bug 1835668

I'm actually removing the lock option from the menu for 20.04 to help reduce any confusion. Locking a live session can be confusing for users, which is why we have disabled this option in the past.

From 19.10 and forward, it is possible to simply turn the locking option back on via the Screensaver settings, Lock Screen tab. The menu option can be found by right-clicking the Whiskermenu icon and navigating to Properties > Commands. The session can also be locked with Super + L or Ctrl + Alt + Del.