Install Qt 6 using MSYS2

pacman -Syu
pacman -S base-devel
pacman -S mingw-w64-x86_64-qt-creator
pacman -S mingw-w64-x86_64-qt6-base
pacman -S mingw-w64-x86_64-qt6
pacman -S mingw-w64-x86_64-clang
pacman -S mingw-w64-clang-x86_64-toolchain
pacman -S mingw-w64-x86_64-clang-tools-extra
pacman -S mingw-w64-x86_64-gdb

Optional Dependencies:

pacman -S mingw-w64-x86_64-cmake
pacman -S mingw-w64-x86_64-gdb
pacman -S mingw-w64-x86_64-ninja
pacman -S mingw-w64-x86_64-qbs
pacman -S mingw-w64-x86_64-qt6-doc
pacman -S mingw-w64-x86_64-qt6-quicktimeline
pacman -S mingw-w64-clang-x86_64-tidy

References
https://wiki.qt.io/MSYS2
https://packages.msys2.org/package/mingw-w64-x86_64-qt-creator
https://packages.msys2.org/package/mingw-w64-x86_64-qt6-base
https://packages.msys2.org/group/mingw-w64-x86_64-qt6
https://packages.msys2.org/package/mingw-w64-x86_64-clang
https://packages.msys2.org/group/mingw-w64-clang-x86_64-toolchain
https://packages.msys2.org/package/mingw-w64-x86_64-clang-tools-extra
https://packages.msys2.org/package/mingw-w64-x86_64-gdb
https://packages.msys2.org/package/mingw-w64-clang-x86_64-tidy?repo=clang64

Encoding of readAllStandardOutput() QProcess

    ...
    output = bytearray(self.process.readAllStandardOutput())
    output = output.decode(self.GetCMD_Encoding())
    print (output)

def GetCMD_Encoding(self):

    CMD = QProcess(self)
    CMD.setProcessChannelMode(QProcess.MergedChannels)
    CMD.start("C:\Windows\System32\chcp.com")
    CMD.waitForReadyRead()
    output = bytearray(CMD.readAllStandardOutput())
    output = output.decode("ascii")
    output = output[18:]
    return "cp" + output

References
https://stackoverflow.com/questions/41761132/pyqt-qprocess-readallstandardoutput-encoding
https://stackoverflow.com/questions/57663191/how-to-convert-a-qbytearray-to-a-python-string-in-pyside2

Get return value and PID of spawned process using QProcess

import sys
from PyQt4 import QtGui, QtCore
from PyQt4.QtCore import QProcess

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)

    command = "./testCommand.py"
    args = [""]

    #"regular" startDetached : give two arguments, get a boolean
    process=QProcess()
    re=process.startDetached("ls",["."])
    print(re)
    print(type(re))

    #"overload" startDetached : give three arguments, get a tuple(boolean,PID)
    process2=QProcess()
    re,pid=process2.startDetached("ls",["."],".")
    print(re,pid)
    print(type(re),type(pid))

References
https://stackoverflow.com/questions/31519215/pyqt4-qprocess-startdetached-cant-get-return-value-and-pid-of-spawned-proce

Use QProcess to run a program

if self.mosquitto_process is None:
    self.mosquitto_process = QProcess()
self.mosquitto_process.start("mosquitto.cmd")
self.port = utils.pick_free_port()
    _logger().debug('starting server process: %s',
                    ' '.join([self._interpreter, server.__file__,
                              str(self.port)]))
    self._process = QtCore.QProcess()
    self._process.readyRead.connect(self._on_ready_read)
    self._process.setProcessChannelMode(self._process.MergedChannels)
    self._process.finished.connect(self._on_finished)
    self._process.stateChanged.connect(self._on_state_changed)
    self._process.start(
        self._interpreter, (server.__file__, str(self.port)))
proc = QProcess()
    proc.start(*py_proc('print("Hello World")'))
    dev = qtutils.PyQIODevice(proc)
    assert not dev.closed
    with pytest.raises(OSError) as excinfo:
        dev.seek(0)
    assert str(excinfo.value) == 'Random access not allowed!'
    with pytest.raises(OSError) as excinfo:
        dev.tell()
    assert str(excinfo.value) == 'Random access not allowed!'
    proc.waitForFinished(1000)
    proc.kill()
    assert bytes(dev.read()).rstrip() == b'Hello World'

References
https://programtalk.com/python-examples/PyQt5.QtCore.QProcess/