Как установить текст в другом окне

Пожалуйста всегда публикуйте минимально-воспроизводимый пример, который включает все модули для запуска приложения. Импорты также показывайте.

import sys                                                                       # <<<<<
import inspect                                                                   # <<<<<
import os.path                                                                   # <<<<<
from pathlib import Path                                                         # <<<<<
from PyQt5 import QtCore, QtGui, QtWidgets                                       # <<<<<
from PyQt5.Qt import *                                                           # <<<<<

from create_new_file_window import Ui_CNFWindow                                  # <<<<<
from ide_ui import Ui_MainWindow                                                 # <<<<<


class CnfWindow(QtWidgets.QMainWindow, Ui_CNFWindow):
    def __init__(self, parent):
        super().__init__()
        self.setupUi(self)
        self.setWindowTitle("CNFWindow")
        
        self.path = None                                                         # <<<<<
        self.parent = parent                                                     # <<<<<

        self.button_confirm_create_new_file.clicked.connect(
            self.create_new_file)

    def create_new_file(self):
        filename = inspect.getframeinfo(inspect.currentframe()).filename
        path = os.path.dirname(os.path.abspath(filename))

        self.path = f"{path}\\{self.name_of_new_file_input_window.text()}.py"    # <<<<<
        open(self.path, "a").close()                                             # <<<<<
        self.parent.path_of_the_current_file_label_bottom.setText(self.path)     # <<<<< !!!
        self.hide()


class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
        self.setWindowTitle("IDE")

        self.process = None
        self.new_window = None

        self.code_entry_window.setDisabled(True)
        self.timer = QtCore.QTime()
        self.result_of_program_execution_window.hide()

        self.button_new_file.triggered.connect(self.new_file)
        self.button_open_file.triggered.connect(self.open_file)
        self.button_save_as.triggered.connect(self.save_as_file)
        self.button_run.triggered.connect(self.run_code)
        self.button_stop.triggered.connect(self.stop_code)

        self.button_save.triggered.connect(self.save_file)
        self.button_new_window.triggered.connect(self.create_new_window)
        self.button_close_window.triggered.connect(self.close_new_window)
        self.button_exit.triggered.connect(self.exit_the_program)
###
# ?        self.button_hide_result_window.triggered.connect(self.hide_result_window)

        self.cfn_window = CnfWindow(self)                                                 # <<< + self

    # -------------------------- BEGIN MENU <FILE> ----------------------------
    def new_file(self):
        self.cfn_window.name_of_new_file_input_window.clear()  # +++
        self.cfn_window.show()
        self.code_entry_window.setDisabled(False)

        # self.code_entry_window.setDisabled(False)
        # cfn_window.hide()
        
        self.path_of_the_current_file_label_bottom.setText('BEGIN MENU <FILE>: New File')  # <<<<<

    def open_file(self):
        path = QFileDialog.getOpenFileName(self, "Save file", "",
                                           "All files (*.*)")[0]
        if path:
            try:
                with open(path, "r") as file:
                    self.code_entry_window.setPlainText(file.read())
            except Exception as e:
                QtWidgets.QErrorMessage().showMessage(str(e))

        self.code_entry_window.setDisabled(False)
        self.path_of_the_current_file_label_bottom.setText(path)

    def save_file(self):
        try:
            with open(f"{self.path_of_the_current_file_label_bottom.text()}", "w") as save_file:
                save_file.write(self.code_entry_window.toPlainText())
        except IOError:
            pass

    def save_as_file(self):
        path = QFileDialog.getSaveFileName(self, "Open file", "",
                                           "All files (*.*)")[0]
        if path:
            try:
                with open(path, "w") as file:
                    text_on_current_file = self.code_entry_window.toPlainText()
                    file.write(text_on_current_file)
            except Exception as e:
                QtWidgets.QErrorMessage().showMessage(str(e))

        self.path_of_the_current_file_label_bottom.setText(path)

    def create_new_window(self):
        if self.new_window is None:
            self.new_window = MainWindow()
            self.new_window.show()
        else:
            self.new_window.close()
            self.new_window = None

    def close_new_window(self):
        self.new_window.close()
        self.new_window = None

    def exit_the_program(self):
        self.close()
    # -------------------------- END MENU <FILE> ------------------------------

    # --------------------------- BEGIN MENU <RUN> ----------------------------
    def message(self, string):
        self.result_of_program_execution_window.append(string)

    def run_code(self):
        self.save_file()
        self.result_of_program_execution_window.show()
        self.result_of_program_execution_window.clear()
        if self.process is None:  # No process running.
            self.message("[Started]\n")
            self.process = QProcess()
            self.process.readyReadStandardOutput.connect(self.handle_stdout)
            self.process.readyReadStandardError.connect(self.handle_stderr)
            self.process.started.connect(self.timer.start)
            self.process.finished.connect(self.finished_code)
            self.process.start("python", [f"{self.path_of_the_current_file_label_bottom.text()}"])

    def handle_stderr(self):
        data = self.process.readAllStandardError()
        stderr = bytes(data).decode("utf8")
        self.message(stderr)

    def handle_stdout(self):
        data = self.process.readAllStandardOutput()
        stdout = bytes(data).decode("utf8")
        self.message(stdout)

    def finished_code(self):
        procTime = self.timer.elapsed()
        self.message(f"[Finished in {procTime / 1000}s]")
        self.process = None

    # TODO: Try/Except на процесс (при втором нажатии вылетает ошибка)
    def stop_code(self):
        self.process.kill()
    # -------------------------- END MENU <RUN> -------------------------------

    # Program closure processing
    def closeEvent(self, event):
        self.save_file()
        reply = QMessageBox.question(self, 'Window Close',
                                     'Are you sure you want to close the window?',
                                     QMessageBox.Yes | QMessageBox.No,
                                     QMessageBox.No)
        if reply == QMessageBox.Yes:
            event.accept()
        else:
            event.ignore()

    def hide_result_window(self):
        self.result_of_program_execution_window.hide()


if __name__ == "__main__":
    application = QtWidgets.QApplication(sys.argv)
    main_window = MainWindow()
    main_window.show()
    sys.exit(application.exec_())