It cannot be done directly from Synapse settings, but you can do it manually by editing Synapse configuration.

1. Close Synapse
2. Edit ~/.config/synapse/config.json
3. Set activate to Super_L

{
  "ui" : {
    "shortcuts" : {
      "activate" : "Super_L",
      ...
    }
  }
}

There is a disadvantage of this solution. You basically can’t use any other global key combinations with Win key, because it will always trigger Synapse.

If that is a problem you can use xcape to assign an additional one-click function to a modifier key.

xcape -e 'Super_L=Super_L|space'

There is a handy feature in Windows, when you type Win+. a selector for Emoji and other Unicode characters will appear.

You can install a similar app in Arch Linux using gnome-characters package.

sudo pacman -S gnome-characters

Now you can mimic the Windows feature and assign a global hotkey for Win+. to execute gnome-characters.

Using xinit you can start applications without even starting a window manager. There is a sample in Arch Linxux wiki, but you may notice that Chromium does not fill full screen.

With the example below a specific site is started in kiosk mode taking whole screen. Change the size based on your display.

exec chromium --app=https://example.com --kiosk --window-position=0,0 --window-size=1366,768

Insert SD card to your system.

sudo fdisk -l
sudo fdisk /dev/sdX

Create partitions.

• Clear partitions (o)
• Create boot partition (n, p, 1, enter, +500M, t, c)
• Create system partition (n, p, 2, enter, enter)
• Write partitions (w)

sudo mkfs.vfat /dev/sdX1
sudo mkfs.ext4 /dev/sdX2

Mount new partitions.

sudo mkdir /mnt/boot/
sudo mkdir /mnt/root/

sudo mount /dev/sdx1 /mnt/boot/
sudo mount /dev/sdx2 /mnt/root/

Download and install Arch Linux ARM.

wget http://os.archlinuxarm.org/os/ArchLinuxARM-rpi-aarch64-latest.tar.gz
sudo su
tar zxvf ArchLinuxARM-rpi-aarch64-latest.tar.gz -C /mnt/root
mv /mnt/root/boot/* /mnt/boot
sync
umount /mnt/boot/
umount /mnt/root/

Remove SD card, insert it into Raspberry PI and boot it to complete the installation.

pacman-key --init
pacman-key --populate archlinuxarm
pacman -Syu

Install autorandr.

sudo pacman -S autorandr

Save current configuration. If you are on notebook you can eg. call it mobile.

autorandr --save mobile

Now connect you external monitor. Change the monitor settings as you wish and save it.

autorandr --save docked

From now on, when you connect external monitor it will automatically switch to it. If you disconnect it it will revert back internal monitor only.

sudo pacman -S solaar
sudo groupadd plugdev
sudo usermod -a -G plugdev your_username

See Arch Wiki for details.