Currently running KDE-Plasma-5.23.5 (X backend)/ KDE-Frameworks-5.90.0 / QT-5.15.3
I can assert that this used to work perfectly but am unfortunately unable to assert from which version of what the problem started to occur systematically.
Whatever the qt5 application I launch (kmail, kate, konsole, dolphin, qtdesigner…) I am no longer able to key in the â ä ë ê î ï ô ö ü û (as well as corresponding uppercase) characters. (usually possible via hitting the dedicated dead key then the desired vowel)
Keying any other directly accessible accentuated character works fine.
I suspect this problem to be restrained to qt5-ed apps since it does not impact non qt5-ed applications such as The-Gimp, Firefox, Chromium, Yoshimi (fltk), my Arduino prototyping platform, audacity… all launched from the same user under the same DE.
UPDATE 1 / XMODIFIERS :
Curiously enough, If I export XMODIFIERS= before launching my DE, or even within some konsole session, then, if I launch kate manually (via bash), the problem does not occur.
It however still occurs when starting kate from the KDE menu or clicking on its icon.
Therefore my problem would become, how should I set XMODIFIERS so that whatever qt5 app could automagically honour it ?
BTW, unless I export it explicitly, this variable is not part of the environment when my DE is running.