SUMMARY
Pressing the ESC key doesn't also turn off the keyboard's backlight on laptops that have a illuminated (backlit) keyboard

STEPS TO REPRODUCE
1. Use a laptop that has an illuminated (backlit) keyboard or maybe a desktop with such a keyboard.
2. Make sure that the keyboard backlight is not set to 'Off' in the 'Brightness and Color' widget.
3. Lock the screen.
4. Press the ESC key.


OBSERVED RESULT
After the ESC key is pressed:
 1. The screen is turned off.
2. The keyboard's backlight is not turned off.

EXPECTED RESULT
The keyboard's backlight is turned off too.


SOFTWARE/OS VERSIONS
Linux (Debian 13 - unstable repository)/KDE Plasma:
KDE Plasma Version: 6.3.2
KDE Frameworks Version: 6.11.0
Qt Version: 6.8.2
Kernel Version: 6.12.17-amd64 (64-bit)
Mesa  Version: 25.0.0-1
Graphics Platform: Wayland


HARDWARE SPECIFICATIONS
Hardware: Laptop Dell Inspiron 5770 (17" 1080p@60Hz screen)
CPU: Intel® Core™ i5-8250U CPU @ 1.60GHz
GPU 1: Intel® UHD Graphics 620 (main, Vulkan capable)
GPU 2: AMD Radeon R5 M465 Series
RAM: 8 GiB (7.7 GiB usable)


ADDITIONAL INFORMATION
I normally turn the screen off at the lock screen when I know that I will be missing from it for a while.
Even it somebody else is there, that could watch it while I'm gone, it will be useless as nothing is happening, there isn't a screen saver appearing.
So it's better to just be off than continuously show the same image.
That way some power is saved.
Since I'm not using the screen, it's highly likely that I'm not using the keyboard either so it's useless to have the backlight there as on. Even more after pressing the ESC key which most likely nobody presses it by mistake at this screen.
For maximum power saving and consistency, I want that the keyboard's backlight is turned off too.
But similar to the screen waking up when a key is pressed, they keyboard's backlight should be set to the previous value that was set inside Plasma session. So if it was set to off, then leave it off. Otherwise the previous value.