1. Open "KWalletManager"
2. If not existent, create a new folder called "Passwords" by clicking on the clear area and then "New"
3. Open that folder, in here you find multiple folders, one is called "Passwords" in your systems language
4. Right click the "Passwords" subfolder and press "new"
5. Name the entry for example "Keepass", click on the entry and "show content", enter your Keepass Password
6. Create an Appstarter for quick-opening your password storage!

You can create an App Desktop Entry like this, open your Terminal and enter:

When using KeepassXC Flatpak:

cat > ~/.local/share/applications/keepassxc-unlock.desktop <<EOF
[Desktop Entry]
Name=Keepass-unlock
Comment=Unlock your KeepassXC vault
Exec=kwallet-query -r KeepassXC kdewallet | /usr/bin/flatpak run --branch=stable --arch=x86_64 --command=keepassxc --file-forwarding org.keepassxc.KeePassXC --pw-stdin ~/passwords.kdbx
Icon=emblem-encrypted-unlocked
Type=Application
EOF

When using a native package:

cat > ~/.local/share/applications/keepassxc-unlock.desktop <<EOF
[Desktop Entry]
Name=Keepass-unlock
Comment=Unlock your KeepassXC vault
Exec=kwallet-query -r KeepassXC kdewallet | keepassxc --pw-stdin ~/passwords.kdbx
Icon=emblem-encrypted-unlocked
Type=Application
EOF