Any GUI doesn't appear when using PyQGIS standalone application. You have to construct it.
Here is an example:
from qgis.core import *
from qgis.gui import *
from qgis.PyQt.QtWidgets import *
### GUI Construction ###
self._canvas = QgsMapCanvas()
Here is how GRASS should be imported (because of a bug it does not work, see more here, thanks Andrea Giudiceandrea):
OSGeo_folder = r'C:\OSGeo4W'
from grassprovider.Grass7AlgorithmProvider import Grass7AlgorithmProvider
I do not have 3.22 installed yet, so not tested in that version. I have tested this with 3.20.3 installed with the new OSGeo4W installer. If it doesn't work for you I will delete this answer.
Tested workflow is:
Save the following batch file (e.g. pyqgis_grass78.bat):