You can add state to store file and your change function something like that:

  const [files, setFiles] = React.useState({
    neededimage: '',
    wantedimage: ''
  });

  const addImage = (e) => {
    setFiles((files) => {
      return { ...files, [e.target.name]: e.target.files[0] };
    });
  };

Add onChange for your inputs:

      <form>
        <input
          type="file"
          accept="image/*"
          name="neededimage"
          id="file"
          onChange={addImage}
        />
        <input
          type="file"
          accept="image/*"
          name="wantedimage"
          id="file2"
          onChange={addImage}
        />
      </form>

And then append files from state into you formData.

You're trying to access value, perhaps what you wanted to do is to access the files.

<div>
 <input type="file"  accept="image/*" name="neededimage" id="file" />
</div>

With the above input tags, you can access the files property which is an IMMUTABLE array.

const createPost = async (e) => {
    e.preventDefault();
    let formData = new FormData();
    formData.append("needed_image", e.target.files[0]);
    const response = await fetch('http://127.0.0.1:8000/api/createpost/', {
        method: "POST",
        body: formData
    });
};

Again remember that this array is IMMUTABLE therefore you can't modify the content directly. Also the e.target.files[0] is stored as a buffer therefore the returned data is a buffer stored in the formData.

Now as you said you have multiple input to deal with, so in this it is better to create a change handler and attach it both the inputs and use an outer FormData to append.

<div>
    <input type="file"  accept="image/*" name="neededimage" id="neededimage" />
    <input type="file"  accept="image/*" name="wantedimage" id="wantedimage" />
</div>

const neededImage = document.getElementById('neededimage');
const wantedImage = document.getElementById('wantedimage');

const handleFiles = () => {
  const files = [...fileInput.files];
  console.log(selectedFiles);
}

neededimage.addEventListener("change", handleFiles);
wantedImage.addEventListener("change", handleFiles);

One more thing since you want to upload multiple files it is better to allow them all in one input.

<div>
    <input type="file" multiple accept="image/*" name="images" id="images" />
</div>

function uploadMultipleFiles() {
    const formData = new FormData();
    const file = document.getElementById("images")    // all uploaded files
    for (let i = 0; i < file.files.length; i++) {
        formData.append(`image-${i}`, file.files[i]);
    }
}```