QGIS 3.4 Processing Python Scripts folder default configuration is lost

How do I add a python script to QGIS?

In the main QGIS window, go to Plugins ‣ Python Console. Once the console is open, find your script in the Processing Toolbox and double-click it to launch it.
 

How do I change the default save location in QGIS?

You can alter the default saving location through Options > Processing.
 

How do I get the python console in QGIS?

The QGIS Python Console is an interactive shell for the python command executions. It also has a python file editor that allows you to edit and save your python scripts. Both console and editor are based on PyQScintilla2 package. To open the console go to Plugins ‣ Python Console ( Ctrl+Alt+P ).