when run as a standalone script, the script has no idea if there are any selections in the data, hence, there is no inputs since you didn't use an sql expression
http://pro.arcgis.com/en/pro-app/tool-reference/analysis/select.htm
if your intent is to just copy the data to a new location, then the help topic suggests using the Copy tool.
The model runs within the toolbox within ArcMap or Pro, because it knows of the existence of selections on the data. The minute you run the script from outside in a standalone python IDE, the knowledge of what is selected and not selected is not known. To fix this, you would need to provide an sql expression in order to get a 'selection'