unwanted screen blanking with after 'waking up' these strange vertical line(s) with weird characters moving along (photo)

My Lubuntu 22.04 LTS laptop should not go into screen blanking as I have disabled this, but it still happens after a period of inactivity. My system is a Notebook MEDION AKOYA S4220 (MD 99660) with Intel® Pentium® processor N3700 en Intel HD-graphics (1,6 GHz tot 2,4 GHz, 2 MB cache).

In Power Management>Inactive I have the screen blanking disabled by setting the option for action to 'nothing' for 'inactivity' at both the power supply and the battery. Screensaver is disabled.

To address earlier problems with a freezing system, I did change the graphics acceleration to SNA a few days ago, which solved the very frequent system freezes, multiple times a day. Those freezes were very random while working on the laptop.

It has been running a few days now without any problems after I changed the acceleration setting. The only thing that bothered me a bit was the unwanted screen blanking, but this gave no problems because after a key press the screen returned to normal.

Today the screen came up after the blanking with this very weird look after hitting a key and my system does not respond anymore then. I had this problem also before the change to SNA acceleration.

The only way then to get back into my system is by a hard power down, followed by powering it on again.

I have 2 photos attached: one with the whole screen plus one with a detail of it. On these photos one can see a vertical line to the left of the screen with an column of greenish symbols moving in a vertical way. At the edge to the left of the main vertical some specs of pixels can be seen and a bit to the right of the main vertical some more of these pixel clusters can be seen. (The other dusty specs are indeed just dust on my dirty screen).

Screenshot of whole screen with weird vertical line:

Detail of weird vertical line:

My question is threefold:

1. Why does the screen go blank while it should not?
2. Can I prevent the screen from going blank?
3. What is happening with these weird 'characters'/pixel clusters?

Edit 1:

Here's a screen capture of my Power Management screen as used during this behavior:

As you can see the language is not English but Dutch. I have this setting for "Inactief' (Inactive) which lacks in the Power Management screen that is shown at the Lubuntu manual where guiverc pointed me to in the comment below.

I can add to this that, before this weird screen thingy came up, I did NOT have the check-mark for 'Inactiviteitsmonitor inschakelen' (Inactivity monitor switched on). I did set this checkmark only yesterday evening late, so maybe it has something to do with it, though the choice for 'Niets' (Nothing), I thought, should not make a difference in behavior.

Right now I did remove that check-mark again and in the meantime I had a blank screen after inactivity from which I could return in a normal way now. If the strange behavior returnd, I will report here.

Edit 2:

The problem returns even after removing the first checkmark at 'Inactiviteitsmonitor inschakelen' (Inactivity monitor switched on). Alas! So the question remains very relevant.

At least I finally found the answer to my second question (and in doing so solved the core of the issue):

2. "Can I prevent the screen from going blank?"

by making a file:

/etc/X11/xorg.conf

with the following contents:

    Section "ServerFlags"
       Option "BlankTime"   "0"
       Option "StandbyTime" "0"
       Option "SuspendTime" "0"
       Option "OffTime"     "0" 
       Option "dpms"        "false"
    EndSection

This stopped the screen blanking and thus prevented the possibility of the weird phenomenon visible on the photos, which could happen after hitting a key to return to the desktop.

In doing so Question 3) is left unanswered still, but that question has become less relevant as the described phenomenon will not happen anymore.

Question 1) remains unanswered also, as far as the settings in the GUI of Power Management are concerned, because one would expect that these should have the effect of stopping screenblanking, which they don't. But with the above solution to the unwanted screen blanking, this question also becomes less relevant, although it would be nice when the settings in Power Management had the same effect.

My system runs smoothly without freezing now.

PS I found this solution at this place.