我通过将isCancelable设置为false来解决这个问题，因为我无法在覆盖点击时隐藏键盘。我设法在每个关闭对话框的操作中使用函数hideKeyboard()，所以当它等于IME_ACTION_DONE时，正负按钮和编辑器都可以操作。
为了在显示对话框时显示键盘，我添加了以下代码：

dialog.window?.setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_VISIBLE)

下面是我的DialogFragment的代码：

private fun hideKeyboard() {
    val im: InputMethodManager = requireActivity().getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
    im.hideSoftInputFromWindow(quantity.windowToken, 0)
}

private lateinit var quantity: EditText

override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    return activity?.let {
        val builder = AlertDialog.Builder(requireContext())
        val view = layoutInflater.inflate(R.layout.dialog_quantity_input, null)

        isCancelable = false
        quantity = view.findViewById(R.id.quantity)

        builder.setView(view)

        viewModel.selectedProduct.value.let {
            quantity.setText(it?.quantity.toString())
        }

        builder.setTitle("Modifica quantità")

        builder.setPositiveButton("Conferma") { _, _ ->
            ...
            hideKeyboard()
        }

        builder.setNegativeButton("Annulla") { _, _ ->
            hideKeyboard()
        }

        quantity.setOnEditorActionListener { v, actionId, _ ->
            if (actionId == EditorInfo.IME_ACTION_DONE) {
                ...
                hideKeyboard()
                dismiss()
            }
            false
        }

        quantity.requestFocus()

        val dialog = builder.create()
        dialog.window?.setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_VISIBLE)

        return dialog
    } ?: throw IllegalStateException("Activity cannot be null")
}