Standalone PyQGIS application that is able to run a custom script, in this case Proximity.py without the need of a GUI. Also we don't need to set all kinds of environment variables using a batch file: just launch the VS Code project, and off you go. This was created for Windows.
First get OSGeo4W LTR by running install/qgis_deploy_install_upgrade_ltr.ps1 from PowerShell console with administrative rights. Ensure to fetch QGIS LTR. This script will automatically download and install OSGeo4W. You can obviously do this manually as well. Just ensure you get QGIS LTR and the full installation. Also ensure to install everything in C:/OSGeo4W. If not, change the paths in .env and .settings.json, see below.
If the script is failing because of accessrights, you need to temporarily bypass the ExecutionPolicy
Set-ExecutionPolicy -Scope Process -ExecutionPolicy BypassOpen up .env in the root folder and verify that following settings match your installation:
OSGEO4W_ROOT=C:/OSGeo4W
QGIS_CONFIG=qgis-ltr
PYTHON_VERSION=Python39
Open up .vscode/settings.json and verify that the path in python.defaultInterpreterPath exists. If it doesn't, update it to match your configuration. You probably need to update PYTHON_VERSION in .env as well.
I've included an example geometry in the test folder: it contains a number of airports in the netherlands. From VS Code select the Launch configuration and hit F5. It'll execute main.py, which in turn executes the Proximity.py script on that test geometry and outputs a rasterized tif.
This should be enough to get you going. Enjoy!
This is based on work by @isogeo: https://github.com/isogeo/isogeo-plugin-qgis/blob/master/.vscode/settings.json as well as various posts on the QGIS stackexchange forum and in particular Kadir Şahbaz: https://gis.stackexchange.com/questions/421329/pyqgis-outside-gui-module-qgis-processing-has-no-attribute-run
It would be great if the QGIS team at one point in the future, would integrate all this in their API/SDK to make this whole process seamless :)