JSFiddle - React, Tailwind, and code Playground

JavaScript

const input = [  
  {  
    "type": "typeA",  
    "label": "labelA",  
    "placeholders": ["b", "a", "r"]  
  },  
  {  
    "type": "typeB",  
    "label": "labelB",  
    "placeholders": ["x", "y", "z"]  
  },  
  {  
    "type": "typeA",  
    "label": "labelAAA",  
    "placeholders": ["a", "b", "c"]  
  }  
];  
 //You can See example here
 //https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce
const output = input.reduce((acc, item) => {  
  // Find the existing group for the current item's type  
  const group = acc.find(g => g.type === item.type);  
  
  // If the group exists, add the item to it  
  if (group) {  
    group.items.push({  
      label: item.label,  
      placeholders: item.placeholders  
    });  
  } else {  
    // If the group doesn't exist, create a new one and add it  
    acc.push({  
      type: item.type,  
      items: [  
        {  
          label: item.label,  
          placeholders: item.placeholders  
        }  
      ]  
    });  
  }  
  return acc;  
}, []);  
  
console.log(output);