AFAIR we intentionally disabled it. The reason for this is that due to how the reload mechanism works there are some side-effects which was causing executing certain code twice.
Check commit: git log a49a3103e298fcc437
If you want to enable reloading for development purposes then you can simply change value of use_reloader option to true, Set use_reloader = True in ../web/pgAdmin4.py +154
Restart pgAdmin4 and it should reload server whenever you save the changes in python files.
In fact when you change python code there isn't much you can do, you need to restart the server every time.
For the Javascript code you can have a second console open and run `yarn bundle:watch` and it will regenerate the javascript code and you just need to refresh the webpage on the browser.
In my config_local.py I have made DEBUG_MODE = TRUE
Even then when I make changes to files in the codebase I am not able to see the changes instantly, I gotta restart the server again and again.I dont want to restart the server again and again to see my changes.