We have developed a few PyQGIS standalone applications that bring in `PyQt5.Qtcore, PyQt5.QtGui, and qgis.core` to display map and do custom logics etc. The applications started with QGIS python 2.7 all the way to QGIS python 3.6, over time we found that it is getting increasingly difficult to get the libraries setup correctly and packaging the application. 

I would like to emphasize that these are applications that are completely standalone without needing to open QGIS program, they are NOT inside QGIS's python console.

Now, it is QGIS 3.16 LTR with Python 3.8, after upgrade QGIS, our apps stopped working. The QGIS installation structure changed a lot with this new version, to name a few things for example, `apps/qt5/include` and `apps/qt5/doc` directories are no longer there, and the following imports are no longer working:

    from PyQt5 import QtCore, QtGui
    from PyQt5.QtGui import *
    from PyQt5.QtWidgets import QApplication, QMainWindow, QUndoCommand, QUndoStack, QFileDialog, QVBoxLayout, QAction
    from PyQt5.QtWidgets import QAbstractItemView, QMessageBox, QMenu, QInputDialog, QDockWidget

Does QGIS still intend to support standalone application development or should we abandon these apps and build plugins instead? I could NOT find an up-to-date programmer's guide for developing standalone applications, most of the PDF instruction files on the internet are for much older versions of QGIS.

We look forward to hearing a more definitive answer.