Kubuntu missing screen lock and screen saver settings
Solution 1
Look at System Settings → Desktop Behavior.
Re. a screensaver, that's not included by default because modern screens aren't affected.
But, if you're interested, look at Where are the screensavers.
Solution 2
I have Kubuntu 18.04 - with nVidia drivers..
The problem is that there are TWO places where this is set.
In the setup tool, there is Workspace/Desktop Behavior/Screen Locking - where I can say "Lock screen automatically after:" then enter a time in minutes.
This does not work worth a damn. I can lock the screen manually - but not have it happen automatically.
However, hidden away under Hardware/Power Management/Energy Saving - there is "Screen Energy Saving" and "Switch off after"...which DOES work.
It's not quite the same thing though because it doesn't lock the screen - and it literally turns the video off rather than displaying a blank screen (or whatever) but for me, it's "good enough".
Screen savers no longer exist without you installing a bunch of extra stuff. So your lock screen (if you can get it to work) won't be any of the cool animations we used to have.
Solution 3
There are two settings. The screen locking and screen switch off.
If I want both locking and switch off, it is necessary to switch off the screen after screen locking. Otherwise the lock screen will wake up the screen, which leads to burn-in of the screen (more accurately, image persistence). What works for me is:
- Desktop Behavior → Screen Locking → Activation → Lock screen automatically after → 10 mins
- Power management → Energy Saving → Screen Energy Saving → Switch off after → 15 mins
This specific behavior may be influenced by my proprietary NVIDIA driver.