Q:

Can't use Macbook Air's keyboard and trackpad simultaneously

I'm trying to play some games on my Macbook Air's laptop and Debian 9 Stretch, but my keyboard and trackpad does not work simultaneously. There are solutions to this problem mentioning changing the keyboard properties with xinput. The thing is, my keyboard/trackpad does not have any property related to that, i.e.  "Disable While Typing". 
xinput output:
$ xinput
⎡ Virtual core pointer                      id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ bcm5974                                   id=11   [slave  pointer  (2)]
⎣ Virtual core keyboard                     id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]  
    ↳ Power Button                              id=6    [slave  keyboard (3)]
    ↳ Video Bus                                 id=7    [slave  keyboard (3)]
    ↳ Power Button                              id=8    [slave  keyboard (3)]
    ↳ Sleep Button                              id=9    [slave  keyboard (3)]
    ↳ Apple Inc. Apple Internal Keyboard / Trackpad id=10   [slave  keyboard (3)]
$ xinput --list-props 10
Device 'Apple Inc. Apple Internal Keyboard / Trackpad':
    Device Enabled (139):   1
    Coordinate Transformation Matrix (141): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    libinput Send Events Modes Available (261): 1, 0
    libinput Send Events Mode Enabled (262):    0, 0
    libinput Send Events Mode Enabled Default (263):    0, 0
    Device Node (264):  "/dev/input/event1"
    Device Product ID (265):    1452, 657
$ sudo xinput --list --long "Apple Inc. Apple Internal Keyboard / Trackpad"
Apple Inc. Apple Internal Keyboard / Trackpad   id=10   [slave  keyboard (3)]
    Reporting 1 classes:
        Class originated from: 10. Type: XIKeyClass
        Keycodes supported: 248

A:

This answer on AskUbuntu helped me.
You basically need to do the following:

In directory /usr/share/X11/xorg.conf.d locate the file named something like *-libinput.conf (in my case, it was 40-libinput.conf).

Open it in any text editor and find the Section "InputClass" with Identifier "libinput touchpad catchall"

In this section, add this line: Option "DisableWhileTyping" "false"

Restart your computer.

