I spent several hours to get everything working as I wanted. Here is what I did. I kind of hope someone shows up telling "there is already a tool for that", but at least I was not able to find clear instructions how to do this. Any additions/corrections are welcome.
- Use pyenv on command line to switch between other Python versions and the one included in QGIS
- Use QGIS features from external Python script to visualize and process spatial data
- Use editor of my choice, in this case Visual studio code