The Ctrl+Shift+U shortcut is interfering with the toggle case key of many editors.
The shortcut key is not part of the KDE desktop environment but is part of the ibus system.
Install the application for configuring shortcuts for inputs from the ibus system.
sudo apt install ibus-setup
Run the ibus-setup command as a regular user to start the GUI application.
Open the Emoji tab end delete or change the Unicode code point: entry.
Restart the ibus daemon to make it have effect.
ibus restart
If this does not have effect logout and login from the desktop.