Fcitx5 modifier keys broken after KDE Plasma 6.7 upgrade

Symptom

After pkcon update on KDE Neon (Plasma 6.7, KWin 6.7.0):

• Korean input works
• Shift/Ctrl modifier keys break in some apps
  • Shift + - does not produce _ (underscore)
  • Ctrl + a acts as plain a
  • But Shift + ㅂ → ㅃ (double consonant) works fine
• Disabling fcitx5 fixes modifier keys → input method is the culprit

Root cause: version skew

Fcitx processes keys in two ways:

When forwarding, fcitx must pass modifier (Shift/Ctrl) state back to the compositor. Fcitx 5.1.7 on KWin 6.7.0 drops modifiers during forward. This was fixed in fcitx 5.1.13.

Why only some apps broke

Fcitx communicates with apps via 3 paths:

• konsole: Path ① (D-Bus directly to fcitx daemon, bypassing KWin) → fine
• ghostty (AppImage): No bundled fcitx frontend → falls to Path ② → KWin bug hits directly → broken

The fix: flatpak fcitx5 (5.1.19)

Since apt’s fcitx5 (5.1.7) cannot be upgraded on KDE Neon 24.04, replace only the daemon with flatpak.

1. Install flatpak fcitx5 + Hangul addon

flatpak install flathub org.fcitx.Fcitx5
flatpak install flathub org.fcitx.Fcitx5.Addon.Hangul

Hangul is a separate extension — not included in the main package.

2. Copy existing config

mkdir -p ~/.var/app/org.fcitx.Fcitx5/config/fcitx5
cp -rf ~/.config/fcitx5/* ~/.var/app/org.fcitx.Fcitx5/config/fcitx5/

3. Stop host fcitx, register flatpak autostart

pkill fcitx5
rm -f ~/.config/autostart/org.fcitx.Fcitx5.desktop

cat > ~/.config/autostart/fcitx5-flatpak.desktop <<'EOF'
[Desktop Entry]
Type=Application
Name=Fcitx5 (Flatpak)
Exec=flatpak run org.fcitx.Fcitx5
EOF

4. Environment variables (host → flatpak daemon)

~/.config/environment.d/fcitx5.conf:

GTK_IM_MODULE=fcitx
QT_IM_MODULE=fcitx
XMODIFIERS=@im=fcitx

5. Re-login

Why keep host fcitx5-frontend packages

The flatpak fcitx5 provides the daemon (engine) only. Native host apps need host IM modules (/usr/lib/.../fcitx5-frontend-*.so) loaded into their process to connect via D-Bus.

[ flatpak fcitx5 5.1.19 daemon ]
  ▲                   ▲                    ▲
  │ D-Bus             │ D-Bus              │ Wayland
[host frontend .so]  [host frontend .so]  [AppImage self GTK]
  │                   │                    │
konsole              native apps          ghostty

Required apt packages (flatpak cannot provide these):

sudo apt install fcitx5-frontend-gtk3 fcitx5-frontend-gtk4 \
                 fcitx5-frontend-qt5 fcitx5-frontend-qt6

Watch out: these may be marked auto-removable. Prevent accidental deletion:

sudo apt-mark manual fcitx5-frontend-gtk3 fcitx5-frontend-gtk4 \
                     fcitx5-frontend-qt5 fcitx5-frontend-qt6

When can we switch back?

Once apt’s fcitx5 reaches 5.1.13+, revert:

1. Remove flatpak autostart
2. Restore host fcitx5 autostart
3. Remove flatpak daemon

Summary