CtrlShiftToCtrlSpacebar.json

{
  "title": "Control_L + Shift_L to Control + Space",
  "rules": [
    {
      "description": "Control_L + Shift_L to Control + Space",
      "manipulators": [
        {
          "type": "basic",
          "from": {
            "key_code": "left_shift",
            "modifiers": {
              "mandatory": [
                "left_control"
              ]
            }
          },
          "to_if_alone": [
            {
              "key_code": "spacebar",
              "modifiers": [
                "left_control"
              ]
            }
          ]
        },
        {
          "type": "basic",
          "from": {
            "key_code": "left_control",
            "modifiers": {
              "mandatory": [
                "left_shift"
              ]
            }
          },
          "to_if_alone": [
            {
              "key_code": "spacebar",
              "modifiers": [
                "left_control"
              ]
            }
          ]
        }
      ]
    }
  ]
}

This is the configuration file for the Karabiner 12+ which has to be placed into the ˜/.config/karabiner/assets/complex_modifications directory to take an effect.