How to configure Function keys on laptop Asus FX506HE-HN012 with Ubuntu 21.04

"fn" keys and combinations are implemented by your actual BIOS, and are not controlled by the operating system.

At least for disabling the touchpad, you can do that using a script or just disable tap-to-click.

For example, this is the script I use to disable tap-to-click with a shortcut key:

#!/bin/bash
STATUS=$(gsettings get org.gnome.desktop.peripherals.touchpad tap-to-click)
case $STATUS in
    true )
        gsettings set org.gnome.desktop.peripherals.touchpad tap-to-click false
        gsettings set org.gnome.desktop.peripherals.touchpad click-method 'areas'
        # 2021-07-05 Change also click method: area when tap is off
        # notify-send "Tap-to-click Off"
    ;;
    false )
        gsettings set org.gnome.desktop.peripherals.touchpad tap-to-click true
        gsettings set org.gnome.desktop.peripherals.touchpad click-method 'fingers'
        # notify-send "Tap-to-click On"
    ;;
esac

• Save the contents in a text file, e.g. ~/bin/toggletouchpad.
• Make that file executable: right-click, select the properties tab to set the executable bit.
• Create a shortcut key to toggle the setting, and as command, enter the full path name of the script: /home/<yourlogin>/bin/toggletouchpad (where <yourlogin> stands for your login name).

Remove the comment sign # if you like to see a notification when you change the status.