How to map the 'Mission Control' key to F3 via Karabiner?
Although the proposed solution works, there are better alternatives IMO. To remap mission_control to right_command for example, you can also:

Add a rule to Karabiner-Elements such as:

{
  &quot;type&quot;: &quot;basic&quot;,
  &quot;from&quot;: {
    &quot;key_code&quot;: &quot;mission_control&quot;,
    &quot;modifiers&quot;: {
      &quot;optional&quot;: [
        &quot;any&quot;
      ]
    }
  },
  &quot;to&quot;: [
    {
      &quot;key_code&quot;: &quot;right_command&quot;
    }
  ]
}

or

Go to System preferences -&gt; Mission Control -&gt; Keyboard and Mouse Shortcuts -&gt; Mission Control and select Right Command