How to run Processing algorithms in standalone PyQGIS applications

pyqgis_standalone_processing.py

import sys
from pathlib import Path

from qgis.core import QgsApplication
from qgis.core.contextmanagers import qgisapp

with qgisapp(guienabled=False, sysexit=False):
    # Required before importing processing:
    sys.path.append(str(Path(QgsApplication.prefixPath()) / "python/plugins"))

    import processing
    from processing.core.Processing import Processing

    Processing.initialize()

    result = processing.run(
        "native:stringconcatenation", {"INPUT_1": "Hello ", "INPUT_2": "world!"}
    )

    print(result["CONCATENATION"])

print("Execution only reaches this line because we passed sysexit=False above.")