SUMMARY
Pressing the Scroll Lock key on IBM PC-compatible keyboards fails to toggle on or off the Scroll Lock indicator LED when the keyboard is connected to an IBM-Compatible x86 PC running Linux with KDE Plasma. 

On keyboard models where the keyboard backlight is part of the Scroll Lock LED circuit, this further results in the keyboard backlight not being able to be turned on. This is a critical accessibility issue for visually-impaired users who require the keyboard backlight to be on in order to see the letters on the keys.

STEPS TO REPRODUCE
1.  Boot into any distro of Linux running KDE Plasma, on an IBM-compatible PC with a keyboard that has a Scroll Lock LED.
2.  Press the Scroll Lock key.
3.  Observe the Scroll Lock LED.

OBSERVED RESULT
On pressing the Scroll Lock key, the Scroll Lock indicator LED fails to toggle on or off.

EXPECTED RESULT
When the Scroll Lock key is pressed, the Scroll Lock LED should turn on and emit visible light.
On pressing it again, the Scroll Lock LED should toggle off.

SOFTWARE/OS VERSIONS
Windows:  This bug is not present in any version of Windows or DOS
macOS:  N/A, I do not have a Mac
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma:  Debian GNU/Linux 13 
KDE Plasma Versions: 6.3.5 
KDE Frameworks Versions: 6.13.0
Qt Versions: 6.8.2
Note: The same bug is found in every version of KDE Plasma in every Linux distro I have so far tested, not just Debian 13.

ADDITIONAL INFORMATION

Attempted workarounds:

Under X11: create a bash script to run "xset led on", then get the display manager setup script to run it so that the Scroll Lock LED and keyboard backlight turn on at the login screen so that visually impaired users can see the keys to type the password. While workable, this is beyond the skillset of the average computer user, especially those new to Linux, so it is a clunky workaround at best, rather than a solution.

Under Wayland: I have not found any viable workaround. 
Methods involving brightnessctl or 
'echo 1 > /sys/class/leds/input3::scrolllock/brightness'
are not practical because they require root privileges / sudo, and users with weak eyesight cannot see the keys to type the sudo password because the backlight is not yet on. Also, display manager setup scripts will not run as root under Wayland so they cannot turn on the LEDs at the login screen.  In addition, when using these methods under Wayland, the Scroll Lock LED and keyboard backlight will turn off when the Caps Lock or Num Lock key is pressed.

Possible workaround for both X11 and Wayland: See comment by Pykler in StackExhange article entitled "Why is the Scroll Lock key disabled in Cinnamon/Linux/Xorg?" dated 2014-10-25

DESIRED BUG FIX
Fix KDE Plasma so that the Scroll Lock indicator LED toggles when the user presses the Scroll Lock key.  The user should not have to write shell scripts and edit config files in order to use Scroll Lock.  Implement a GUI setting in KDE Plasma where the user can configure the Scroll Lock LED to be on at the display manager login screen so that visually-impaired users who need the keyboard backlight can see the keys to type the password.