/etc/default/keyboard you can configure the keyboard and also set options. For example here is my favorite keyboard setting:
rpi ~$ cat /etc/default/keyboard
# KEYBOARD CONFIGURATION FILE
# Consult the keyboard(5) manual page.
As you can see with
XKBOPTIONS="caps:escape" I changed the capslock key to work as an additional ESC key. This may also be usable with your keyboard. Description of all available keyboard models, layouts, variants and options is available in
/usr/share/X11/xkb/rules/xorg.lst. Look there at the section
man keyboard you will find:
In Debian systems the default keyboard layout is described in /etc/default/keyboard and it is shared between X and the console.
So the settings are also reflected in X sessions. I can confirm this at least for version Stretch and Buster.