It's been some month since this issue land on GTK app: https://github.com/ghostty-org/ghostty/discussions/8899

Especially for me, I wanted to switch to Ghostty and when I wanted to use ~ I was left why a blank space.

So according to the selected answer the most reliable way of fixing that on KDE, while waiting for a fix, is the following:

first you need to install all needed package for fcitx5 to work

then we update the config

logout / login

you can now enjoy your dead key working again!

So:

sudo pacman -S fcitx5 fcitx5-qt fcitx5-gtk fcitx5-configtool

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Next create / open the config file:

nvim ~/.config/environment.d/im.conf

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Then you can put the config in the im.conf file:

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

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After that you can logout / login and everything should be fine :)

If needed you can check that the layout that use fcitx5 is…