Hi, all. Finally migrated from Kubuntu to Debian 12 over the weekend. It's working great, as I figured it would, with one exception: The system isn't turning the monitors off after 10 minutes. It's blanking them, but they're clearly still on.

One monitor is on an AMD graphics card, the other is on the motherboard Intel adapter.

Debian 12 with KDE Plasma running on Wayland with sddm login. It previously worked fine on Kubuntu (which I believe was running X11). It's a fresh Debian install on a different drive; I didn't overwrite the Kubuntu installation.

In the Energy Saving settings, I have "Screen energy saving" checked with a delay of 10 minutes. (I have "suspend session" turned off - one, because I don't want the computer to sleep or suspend, and two, because when I woke it up again, the graphics were garbled and I had to reboot.) As I said, it does blank the screens, but they're still clearly on. I want them to go into power save mode.

I've tried running dpkg-reconfigure and selecting sddm, no change. In KDE's background services, I tried turning off KScreen 2, but that didn't help (though I'm not sure if I rebooted after turning it off, now that I think about it).

I found advice somewhere that suggested deleting .config/powermanagementprofilesrc and rebooting; I did that, no change.

I did notice yesterday that the monitors had shut off...after a very long time of being idle. I'm not sure how long, but more than overnight, for certain.

Any advice or suggestions? Unfortunately, searching is difficult, because I get a lot of results where the screen blanks when it shouldn't. I haven't found much for this problem.

I used the same installer on my laptop to do the same migration (also with KDE Plasma and sddm) and it works fine there.