It's always known that the computer will be annoying when it comes to watching movies on Linux. Here's a discussion of how the activity configuration of KDE does not extinguish the screen when watching a movie.
First of all, this is just the implementation of the screen, lock screen problems can not be solved temporarily, my treatment is never lock screen.
Step 1: Create a new activity, named movie.
Step 2: Turn on power Management. Select Activity Settings, select Movie, select Define a special behavior, select never shutdown the screen.
Step 3: Add a shortcut key to the movie activity. I set the CTRL + Shift + M.
Next, when you watch a movie, just press CTRL + Shift + M to switch to movie activity and the screen is not automatically extinguished.
In addition: The GNOME desktop can be implemented through the coffee plug-in full screen without lock screen.
Make use of KDE activity to see the movie without putting out the screen