If you use %1 in the path then it gets replaced with %251 in the dialog box. It seems to work correctly, using the device name in the path, but just displays wrong. I'm using UK localization settings.
%251 is of course the urlencoded representation of %1 but it should be displayed correctly in the unencoded form.
https://cgit.kde.org/kdeconnect-kde.git/commit/?id=7d6e4895208429bd211e2864e525bc7eabdf760b