SUMMARY I can't use a custom keyboard layout for this in Wayland;; SOFTWARE/OS VERSIONS Linux/KDE Plasma: 5.24.4 (available in About System) KDE Plasma Version: 5.93.0 KDE Frameworks Version: 5.93.0 Qt Version: 5.15.3 ADDITIONAL INFORMATION
Not a direct fix for this bug, but in Plasma 6.0 you'll be able configure the screen to automatically turn off after a certain time when the screen is locked. You can set this to a value in the low seconds and use the "Lock session" keyboard shortcut, which defaults to "Meta+L", until Plasma adds a "Turn off screen" shortcut.
You can configure a custom shortcut to turn off the screen by opening System Settings, "Keyboard" -> "Shortcuts" page, "Power Management" category (or search for "screen"), assign your favorite shortcut to "Turn Off Screen". It looks like this has already been possible since 2019, but I just tested this under Wayland and it still works as it should.