EDIT: I am redefining my request, since the word "screensaver" seems to have some negative connotations. So now I am looking for something that will let me launch a full screen static image (.png or .jpeg or similar file) and display it until I come back and hit a key or something. That will do what I need and in particular it will not lock the screen or turn off the signal to the display or activate power management or anything like that.
(This is what I had written previously, please ignore it as it seems to inspire "solutions" that won't work for me and that kind of miss the whole point, I am only leaving it here so the discussion that follows in the first few messages makes sense and because some of the proposed solutions may work for other, even if they don't work for me).
I just started using Ubuntu 24.04 as my main desktop computer and I am looking for a screensaver that turns the full screen area black (or very dark grey) after some period of inactivity but does NOT completely turn off the signal to the display, and that still allows popup notifications to be displayed. So nothing involving lock screens, power management or anything like that, just something that sends a static black or dark grey image to the full screen area until there some activity with the keyboard or mouse. The privacy/security setting in Ubuntu isn't suitable because it stops sending any signal at all; I need it to send an all-black or very dark image to the display.
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