I’m on an old Apple Magic Keyboard, so I have no right Ctrl button. On the left are Fn, Ctrl, Option/Alt and Command/Win on the right are Command,/Win and Option/Alt. None of the layouts quite matches what my keyboard has.
By the same token, on macOS it was Command + e to type é with the Intl keyboard layout. On KDE Ctrl is generally like Command on MacOS in that Ctrl + E is not bound, but Command + E, and Alt + E are already bound to things.
What I would like is to have Left Ctrl + e let me type the diacritics (accents). Does anyone know how to do this?