気を付けるポイントとしては、

• SortableItem用にidを定義する必要がある
• touchActionのnoneを設定しないとモバイル操作がうまくいかない

以下実装例

<DndContext
  sensors={sensors}
  collisionDetection={closestCenter}
  onDragEnd={handleDragEnd}
  modifiers={[
    restrictToVerticalAxis,
    restrictToWindowEdges,
    restrictToParentElement,
  ]}
>
  <SortableContext
    items={ideas.map((idea) => ({ id: idea.id }))}
    strategy={verticalListSortingStrategy}
  >
    <div className='mt-8 w-full grow rounded-3xl bg-gray-100 px-4 py-8 shadow-md'>
      <div className='item-center flex justify-center'>
        <div className='w-full'>
          <TextInput
            id='idea_title'
            type='text'
            variant='noneShadow'
            placeholder='アイデアを入力してください'
            maxLength={100}
            value={newIdeaTitle}
            onChange={(event) => {
              setNewIdeaTitle(event.target.value);
            }}
          />
        </div>

        <div className='ml-4'>
          <button
            className='flex size-9 items-center justify-center rounded-full bg-gray-300 p-2 text-white shadow-md hover:bg-gray-500'
            onClick={handleAddIdea}
          >
            <PlusIcon />
          </button>
        </div>
      </div>

      <ul className='mt-8'>
        {ideas.map((idea) => (
          <SortableItem
            key={idea.sort}
            id={idea.id}
            ideaId={idea.ideaId}
            title={idea.title}
            handleCreateMemoButtonClick={handleCreateMemoButtonClick}
            handleDeleteIdea={handleDeleteIdea}
          />
        ))}
      </ul>
    </div>
  </SortableContext>
</DndContext>

const SortableItem = ({
  id,
  ideaId,
  title,
  handleCreateMemoButtonClick,
  handleDeleteIdea,
}: SortableItemProps): JSX.Element => {
  const {
    attributes,
    listeners,
    setNodeRef,
    transform,
    transition,
    isDragging,
  } = useSortable({ id });

  const style = {
    transform: CSS.Transform.toString(transform),
    transition,
    touchAction: 'none',
  };

  return (
    <>
      <li
        ref={setNodeRef}
        style={style}
        {...attributes}
        {...listeners}
        className={`my-2 flex items-center justify-between bg-white p-2 shadow
          ${isDragging ? 'cursor-grabbing' : 'cursor-grab'}`}
      >
        <span>{title}</span>
        <div className='ml-auto flex gap-4'>
          <CircleButton
            size='small'
            variant='tertiary'
            onClick={() => {
              handleCreateMemoButtonClick(title);
            }}
          >
            <PencilEditIcon className='size-4' />
          </CircleButton>
          <CircleButton
            size='small'
            variant='gray'
            onClick={async () => {
              await handleDeleteIdea(ideaId);
            }}
          >
            <TrashIcon className='size-4' />
          </CircleButton>
        </div>
      </li>
    </>
  );
};