Как исправить зависание програмы PyQt?

Взял сервер (написанный на PyQt !) со своего ответа Передача данных через socket в локальной сети python

В вашем примере поменял импорты под себя (PyQt5) и свой порт 9090.

Все работает !

#from PySide2.QtCore import (QCoreApplication, QMetaObject, QObject, QPoint, QRect, QSize, QUrl, Qt)
#from PySide2.QtGui import (QBrush, QColor, QConicalGradient, QCursor, QFont, QFontDatabase, QIcon, 
#    QLinearGradient, QPalette, QPainter, QPixmap, QRadialGradient)
#from PySide2.QtWidgets import *

import sys
from PyQt5 import QtCore, QtWidgets
from PyQt5.Qt import *

import asyncio
from asyncio import transports
from asyncqt import QEventLoop


#from app.interface import Ui_MainWindow
class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        if MainWindow.objectName():
            MainWindow.setObjectName(u"MainWindow")
        MainWindow.resize(372, 645)
        self.centralwidget = QWidget(MainWindow)
        self.centralwidget.setObjectName(u"centralwidget")
        self.verticalLayout = QVBoxLayout(self.centralwidget)
        self.verticalLayout.setObjectName(u"verticalLayout")
        self.message_box = QPlainTextEdit(self.centralwidget)
        self.message_box.setObjectName(u"message_box")
        self.message_box.setReadOnly(True)

        self.verticalLayout.addWidget(self.message_box)

        self.message_input = QLineEdit(self.centralwidget)
        self.message_input.setObjectName(u"message_input")

        self.verticalLayout.addWidget(self.message_input)

        self.message_button = QPushButton(self.centralwidget)
        self.message_button.setObjectName(u"message_button")

        self.verticalLayout.addWidget(self.message_button)

        MainWindow.setCentralWidget(self.centralwidget)

        self.retranslateUi(MainWindow)

        QMetaObject.connectSlotsByName(MainWindow)
    # setupUi

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(QCoreApplication.translate("MainWindow", u"Это ваш Клиент", None))
        self.message_box.setPlaceholderText(QCoreApplication.translate("MainWindow", u"Connecting...", None))
        self.message_input.setPlaceholderText(QCoreApplication.translate("MainWindow", u"Type your message here...", None))
        self.message_button.setText(QCoreApplication.translate("MainWindow", u"Send", None))


class ClientProtocol(asyncio.Protocol):
    transport: transports.Transport
    window: 'MainWindow'

    def __init__(self, chat_window: 'MainWindow'):
        self.window = chat_window

    def data_received(self, data: bytes):
        decoded = data.decode()
        self.window.append_text(decoded)

    def send_data(self, message: str):
        encoded = message.encode()
        self.transport.write(encoded)

    def connection_made(self, transport: transports.Transport):
        self.window.append_text("Подключено")
        self.transport = transport

    def connection_lost(self, exception):
        self.window.append_text("Отключено")


class MainWindow(QMainWindow, Ui_MainWindow):
    protocol: ClientProtocol

    def __init__(self):
        super().__init__()
        self.setupUi(self)

        self.message_button.clicked.connect(self.button_handler)

    def button_handler(self):
        message_text = self.message_input.text()
        self.message_input.clear()
        self.protocol.send_data(message_text)

    def append_text(self, content: str):
        self.message_box.appendPlainText(content)

    def build_protocol(self):
        self.protocol = ClientProtocol(self)
        return self.protocol

    async def start(self):
        print(f'\n async def start(self): Привет \n')
        self.show()

        event_loop = asyncio.get_running_loop()

        coroutine = event_loop.create_connection(
            self.build_protocol,
            "127.0.0.1",
            9090                                                         # 8888
        )

        await asyncio.wait_for(coroutine, 1000)


app = QApplication(sys.argv)                                       # sys.argv    PyQt5

loop = QEventLoop(app)
asyncio.set_event_loop(loop)

window = MainWindow()
loop.create_task(window.start())
loop.run_forever()