"Blank screen" after inactivity not really blank - mouse cursor stays

There is something wrong with the Power saving's "Blank screen". I've recently upgraded to 20.04 from 18.04. Blank screen is set to activate after 4 mins of inactivity. The problem is that the screen is going blank, but the mouse cursor is still shown and prevents monitor from suspending.

Any idea how to fix that?

The mouse showing is a symptom, not a cause of the screen not going into power saving mode. I believe (but can't prove) there are bugs in the high level screen saver settings that prevent the low level X11 screen saver from properly trigger power saving.

Also, some applications (video viewers, games, some full screen apps) disable screen blanking and power saving and the screen blanker does not automatically re-enable it reliably.

At a low level, you can check this with the xset command: xset -q and look for the DPMS settings:

  DPMS (Energy Star):
  Standby: 300    Suspend: 400    Off: 600
  DPMS is Enabled
  Monitor is On

• If DPMS is disabled, you can enable it with xset +dpms
• If you want to change the timings (in seconds), use for example xset dpms 300 400 600 ; the times correspond to increasingly deeper levels of power saving, which was relevant for CRTs but is probably moot for LCDs and other modern screens that power back on instantly.
• If you just want to force the screen off immediately, xset dpms force off

Note, however, that the the last item will only work briefly if you try to activate it with a mouse. A few second delay before it will give you time to let go of the mouse before it runs.

In the past, you could set these things and forget them and it would work. However, modern graphical shells mess with them, and don't provide a direct way to set them, and a few applications change them as well, so setting them directly is not reliable unless you reset them to what you want periodically. Also, some screen blankers don't use the timeout settings in DPMS and zero those, and then run dpms force off themselves when they feel like it.

But if your screen is not powering down, you can at least use these commands to diagnose the issue.

Then, Kernel must have a different compatibility factor with the mouse touchpad, Try installing Additional Kernel 5.8 then switch to that kernel from the boot menu and see if it works.

Kernel Download Link:

https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.8/amd64/

Installing command:

$ sudo dpkg -i linux-modules-5.8.0-050800-generic_5.8.0-050800.202008022230_amd64.deb

If this issue comes after upgrade then Try to check if all upgrade using below commands, see if it helps.

$ sudo dpkg --configure -a

$ sudo apt --purge autoremove

$ sudo apt update --fix-missing

$ sudo reboot

If above steps doesn't work then there are below factors might possible for this issue.

1. Some Application is still running in the background which causing this.
2. Video or Hardware Driver Issue like incompatible video driver or Mouse touchpad driver which doesn't get suspended.

but before that please show us the output of this command (to check kernel version)

$ uname -r