Install xtrlock by entering the following commands in the terminal:
sudo apt update sudo apt install xtrlock
Description:
Minimal X display lock program
xtrlock is a very minimal X display lock program, which uses nothing except the Xlib library. It doesn't obscure the screen, it is completely idle while the display is locked and you don't type at it, and it doesn't do funny things to the X access control lists.
Version: 2.8
Section: universe/x11