Hello,
I would like to create a python toolbox, but in arcgis pro there is no longer the button to load the source script.
I wonder how i can define the source script ?
Creating the toolbox is done in Arctoolbox, then you add a tool and specify the script there.
Can you show where the issue is?
I think you are confusing a custom toolbox with a python toolbox. You can't add existing scripts to a python toolbox, you need to edit it and write a Tool class.