Seeing unwanted screen dimming after update to 21.10
After updating from 21.04 to 21.10 last week I began to experience issues related to screen dimming. I have a Dell laptop, docked running an external 24 inch dell monitor. I had never used the screen dimming because it did not seem to work previously. I has tried enabling it on this config but found the screen was either on or blank with no dimming. I must have left that option checked in the power management "on AC power" settings, and after the update I found that if I left my computer idle for extended amounts of time (more than an hour) I would return to find the screen powered, but the image was dimmed to about 5-10% of its usual brightness. This is functionally useless because although I can see the shadows of the windows on the screen, it is unreadable.
Environment: Dell 5430 core i7 w/ Intel HD 4000 graphics. Ubuntu Mate 21.10 (mate 1.26.0), gnome desktop, Compiz configured settings.
Troubleshooting.: Of course, I checked the power settings and found that the "Dim screen when idle: was checked in the power management settings. I unchecked it, applied, restarted and waited. The problem persisteted. I returned to the power management settings and the item was still unchecked. I also made sure any dimming options (including dimming key backlight) were unchecked as well. I tried suspending (sleeping) the system while in this state. Upon waking there was stil the same issue. I tried sleeping, undocking, and opening the laptop lid and the problem continued on the laptop LCD (note, if I was not clear earlier, in its daily configuration the laptop is docked and only uses the external monitor). I could do a forced shutdown with the power key and then system would boot ok, but still problem would return. I ran all updates again. so help. I went to the display properties, all were their usual settings, but I changes a setting and clicked apply in order to be sure the monitor settings had been saved successfully as well. Still no change to the issue.
Any ideas? I think I've covered most the correct troubleshooting steps. I have a feeling this may be an issue with the fact that dimming didn't used to work and in the latest version someone tried to solve that and it is still having bugs...not to mention is unresponsive to turning off that settings.
It is a side-effect of bugs in mate-screensaver and mate-menus. See bug 1943369 and bug 1947905. Please subscribe to both and mark yourself as affected.
Possible workaround is to remove MATE Screensaver and temporary replace it by XScreenSaver:
sudo apt-get purge --autoremove mate-screensaver
sudo apt-get install xscreensaver
systemctl --user enable xscreensaver.service
systemctl --user start xscreensaver.service
then test it using Ctrl+Alt+L.
Reverting to default screensaver is possible by
systemctl --user disable xscreensaver.service
sudo apt-get purge --autoremove xscreensaver
sudo apt-get install mate-screensaver ubuntu-mate-desktop ubuntu-mate-core
Via https://ubuntu-mate.community/t/21-10-screen-dim-problem/24710/7 .