There are 3 folders in Debian for your current KDE user configuration:
~/.config
~/.local
~/.kde
You have to take a look what you need, you don't need all the folders, because there are also the folders of your installed programs/apps.
I'm not sure if you can export it one-to-one like that and import it from Arch to Debian easily, or if it's unfortunately better to set it up completely from scratch again on your new Debian.
Take also a look at Plasma Customization Saver.
These are the files for my KDE with Dolphin backup and export, to a second desktop:
KDE-Dolphin main configuration:
~/.config/dolphinrc
~/.local/share/kxmlgui5/dolphin
~/.local/share/dolphin/view_properties
~/.local/share/kxmlgui5/dolphin/dolphinui.rc.
KDE-Dolphin sidebar and bookmark configuration:
~/.local/share/user-places.xbel
KDE-Dolphin keyboard shortcuts configuration:
~/.config/kdeglobals
~/.config/kglobalshortcutsrc
~/.config/khotkeysrc
This is an old description and differently depending on the system and no longer up-to-date:
The majority of KDE settings are stored in hidden directories under your home folder. You can copy these directories to your new Debian installation. The main directories you want to copy are this:
~/.config
- Contains various configuration files for KDE applications and the Plasma desktop
~/.local/share/plasma
- Contains the desktop and panel settings
~/.local/share/kwin
- Contains window manager settings, including window decorations and effects
~/.local/share/color-schemes
- Contains your custom color schemes
~/.local/share/aurorae
- Contains window decoration themes
~/.local/share/fonts
- Contains any custom fonts you might have installed
~/.local/share/plasma/desktoptheme
- Contains your custom desktop themes
~/.local/share/sddm
- Contains the SDDM (login manager) theme settings
~/.local/share/ksplash
- Contains the splash screen settings