Windows: Key to Launch or Switch App
This page shows you how to set a key to switch to your favorite app, for Microsoft Windows. For example, set F8 to switch to browser. For Mac or Linux, see How to Set Key to Switch to Browser
There are many ways to setup one single key to switch/launch a app. We'll cover the best way first.
Why Alt Tab is No Good
Key to Launch or Switch to App, Best Method
This is the best method. Simplest and fastest.
In Windows 10, drag and drop the app to Taskbar. Then, the apps on taskbar from left to right will have keys ❖ Window+1, ❖ Window+2, etc.

Now, set up a single key to press the keychords.
Programable Keyboards with Onboard Memory
if you have Programable Keyboards with Onboard Memory or Programable Keypad, you can then assign key such as F8 to do ❖ Window+1 etc, so they are single key presses.
Microsoft PowerToys
If you don't have a programable keyboard, the best way is to use Microsoft PowerToys. [see Microsoft PowerToys]
Create Custom Key Shortcut to Launch App
Create a shortcut to the file (by holding Alt key then drag). Then, right click on the file shortcut and choose “Properties”. There, click the Tab named “Shortcut”, then click the “Shortcut key” field then type a key.
Here's a step-by-step instruction:
Go to desktop. Right click and chose New, then Shortcut.

Then click on a Shortcut, then right click, or press Alt+Enter to bring up its properties.

Then, click the Shortcut tab, click the “Shortcut key” field, then just type a key combo to set a hotkey.

The shortcut must be one of F1, F2 etc, or a key with Ctrl+Alt or Ctrl+Shift .
For some app, this will switch to it if already running (For examples: cmd.exe, Inkscape.), but for some app it'll always launch a new instance.