かなキーで「英数/かな」のトグル切り替え（Karabiner-Elements 11.1.8以上が必要）

karabiner.json

{
  "profiles": [
    {
      "complex_modifications": {
        "rules": [
          {
            "description": "Toggle input source (English or Japanese) by kana key (available since Karabiner-Elements 11.1.8)",
            "manipulators": [
              {
                "conditions": [
                  {
                    "input_sources": [
                      {
                        "language": "ja"
                      }
                    ],
                    "type": "input_source_if"
                  }
                ],
                "from": {
                  "key_code": "japanese_kana"
                },
                "to": [
                  {
                    "key_code": "japanese_eisuu"
                  }
                ],
                "type": "basic"
              }
            ]
          },
          ...          
        ]
      }
    }
  ]
}