SELECT 
  cscart_ab__mb_motivation_item_objects.motivation_item_id, 
  cscart_ab__mb_motivation_item_objects.object_type, 
  GROUP_CONCAT(
    cscart_ab__mb_motivation_item_objects.object_id
  ) as object_ids 
FROM 
  cscart_ab__mb_motivation_item_objects 
WHERE 
  1 
  AND cscart_ab__mb_motivation_item_objects.motivation_item_id IN (1, 2, 3) 
  AND cscart_ab__mb_motivation_item_objects.object_type IN ('C', 'D', 'P') 
GROUP BY 
  cscart_ab__mb_motivation_item_objects.motivation_item_id, 
  cscart_ab__mb_motivation_item_objects.object_type

Query time 0.00026

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.014875922,
    "nested_loop": [
      {
        "read_sorted_file": {
          "filesort": {
            "sort_key": "cscart_ab__mb_motivation_item_objects.motivation_item_id, cscart_ab__mb_motivation_item_objects.object_type",
            "table": {
              "table_name": "cscart_ab__mb_motivation_item_objects",
              "access_type": "range",
              "possible_keys": ["PRIMARY", "mid_otype"],
              "key": "PRIMARY",
              "key_length": "3",
              "used_key_parts": ["motivation_item_id"],
              "loops": 1,
              "rows": 13,
              "cost": 0.00658479,
              "filtered": 100,
              "attached_condition": "cscart_ab__mb_motivation_item_objects.motivation_item_id in (1,2,3) and cscart_ab__mb_motivation_item_objects.object_type in ('C','D','P')"
            }
          }
        }
      }
    ]
  }
}