dotfiles/mac/karabiner/fn-tab_to_cmd-tab.json

{
    "description": "Map fn+tab to cmd+tab",
    "manipulators": [
        {
            "from": {
                "key_code": "tab",
                "modifiers": {
                    "mandatory": [
                        "fn"
                    ]
                }
            },
            "to": [
                {
                    "key_code": "tab",
                    "modifiers": [
                        "left_command"
                    ]
                }
            ],
            "type": "basic"
        }
    ]
}