Using the vanilla kernel did not help, but uninstalling the xf86-video-intel driver solved the issue!!
Thank you very much @manuel !
(And also thanks to @ricklinux and @Trekkie00 for their inputs 
)
4 Likes
Great that it helped! 
On some machines with Intel graphics removing the Intel driver helps, but on some other machines adding the same driver helps.
Not sure why but I’ve seen that many times.
2 Likes
Yes, it is strange considering from what I read that the kernel driver works better to begin with. It must pick up something when the Intel driver is installed that causes the issue.
2 Likes
I have realised that a minor screen tearing I have been experiencing with videos (mpv, VLC, browser videos) for a while now was the result of removing xf86-video-intel.
I have reinstalled the package, and lightdm is back to its “torn” state.
If you had any other ideas I could try, that would be great, but in case keeping the login screen like that would be a bearable compromise to have fully tear-free video playback
On my own (three) computers which have this same problem, I believe that it has something to do with the UEFI/BIOS having some sort of conflict with Linux 5.10.x… All three computers have the same BIOS: InSyde BIOS Version 1.07.03. I believe that this BIOS is causing the problem and I do not know how to upgrade it (which, I believe, would eliminate the problem).
As a consequence, I now run the Linux-lts kernel (which is currently 5.4.95-1) on those three computers.
Of course the lts kernel will eventually be upgraded to 5.10.x and that might cause the problem to reappear.
So, as a “backup to the backup,” I have installed Linux-lts419 (currently 4.19.173-1) from the AUR.
Therefore, I have three kernels installed; the “standard” linux-lts kernel, the linux-lts419 kernel, and the “regular” linux kernel. I have them in that order in GRUB and the lts kernel is the default.
Within another thread, jonathan suggested using his own repository in which he has made available several older maintained lts kernels. Unfortunately, for whatever reason, I was unable to install his repository and get it working (on ANY of those computers).
So I merely installed linux-lts419 directly from the AUR. The problem with doing this? Well, when it upgrades, the process takes about two (2) HOURS!
Fortunately you can do other things while this process is ongoing; as a matter of fact, as I’m typing this, it is being upgraded right now (on another workspace).
Perhaps you might want to try this. At least it has eliminated any screen problems for me without introducing any new problems.
I hope that this recommendation is of some help to you.
Lawrence
1 Like
Thank you so much for your very thorough answer.
Since I also prefer to keep the latest kernel (especially for the gains in power management) I think I will change display manager as a workaround for the time being.
I have successfully moved to using ‘sddm’ in place of ‘lightdm’
Personally, I am using this theme on XFCE, but plenty more are available on github (and on the KDE online “marketplace”, but you have to be careful to make sure to use sddm-only themes, as some feature deeper integration with the plasma desktop and will not do well unless you use KDE)