Karabiner-Elements cannot open new Terminal window unless Terminal already in focus

I am on Catalina 10.15.7 and use Karabiner-Elements 13.3. When I use the rule shown below for opening Terminal nothing happens unless Terminal is in focus (you can see Terminal on the menu bar). Seems like something to do with security permissions. When I run the script itself from within iTerm (not Terminal) I got a pop up asking for allowing "access to control". Once accepted the shortcut worked when either Terminal or iTerm was in focus. Obviously I want the shortcut to work regardless of what is in focus. How to achieve that?

{
  "title": "Open Terminal",
  "rules": [
    {
      "description": "Open Terminal",
      "manipulators": [
        {
          "type": "basic",
          "from": {
            "modifiers": {
              "mandatory": [
                "left_control",
                "left_alt"
              ]
            },
            "key_code": "t"
          },
          "to": [
            {
              "shell_command": "osascript -e 'tell app \"Terminal\"' -e 'do script \"tmux\"' -e 'end tell'"
            }
          ]
        }
      ]
    }
  ]
}