why matplotlib Button not work with pyqt5?

I now want to use the Custom Button function of matplotlib, refer to this document: https://matplotlib.org/stable/gallery/widgets/buttons.html, it works quite well. But when I want to combine it with PyQt5, I first create a main window with a button in it. When the button is clicked, a plot will pop up, but the button in the plot loses its response. code show as below:

import sys

import matplotlib.pyplot as plt
import numpy as np
from matplotlib.widgets import Button
from PyQt5.QtCore import pyqtSlot
from PyQt5.QtWidgets import QApplication, QPushButton, QWidget


class Index:
    ind = 0

    def __init__(self, l, freqs):
        self.l = l
        self.freqs = freqs

    def next(self, event):
        self.ind += 1
        i = self.ind % len(self.freqs)
        ydata = np.sin(2 * np.pi * self.freqs[i] * t)
        self.l.set_ydata(ydata)
        plt.draw()

    def prev(self, event):
        self.ind -= 1
        i = self.ind % len(self.freqs)
        ydata = np.sin(2 * np.pi * self.freqs[i] * t)
        self.l.set_ydata(ydata)
        plt.draw()


class App(QWidget):

    def __init__(self):
        super().__init__()
        self.title = 'PyQt5 button - pythonspot.com'
        self.left = 10
        self.top = 10
        self.width = 320
        self.height = 200
        self.initUI()

    def initUI(self):
        self.setWindowTitle(self.title)
        self.setGeometry(self.left, self.top, self.width, self.height)

        button = QPushButton('PyQt5 button', self)
        button.setToolTip('This is an example button')
        button.move(100, 70)
        button.clicked.connect(self.on_click)

        self.show()

    @pyqtSlot()
    def on_click(self):
        freqs = np.arange(2, 20, 3)
        fig, ax = plt.subplots()
        fig.subplots_adjust(bottom=0.2)
        t = np.arange(0.0, 1.0, 0.001)
        s = np.sin(2 * np.pi * freqs[0] * t)
        l, = ax.plot(t, s, lw=2)

        callback = Index(l, freqs)
        axprev = fig.add_axes([0.7, 0.05, 0.1, 0.075])
        axnext = fig.add_axes([0.81, 0.05, 0.1, 0.075])
        bnext = Button(axnext, 'Next')
        bnext.on_clicked(callback.next)
        bprev = Button(axprev, 'Previous')
        bprev.on_clicked(callback.prev)

        plt.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = App()
    sys.exit(app.exec_())

I want to know why?

In this question: matplotlib event doesn't work when I use button clicked connect in pyqt5, I see that it seems to define a window myself , and then embed matplotlib, but I don't understand why Is there a document that says we must do this?

I tried Macos, linux, windows, it works under macos, but the button doesn't respond under linux and windows. I suspect it has something to do with QCoreApplication::exec: The event loop is already running, but I don't understand why the qt problem affects matplotlib. Is the signal of matplotlib registered to pyqt5?