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

Next create / open the config file:

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

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

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

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

If needed you can check that the layout that use fcitx5 is the same has the one KDE is using, and also you maybe want to auto start it on session startup but for me that was the case by default!

See ya!