General Settings is for when you are accessing lists with NITRO Forms on another site within your tenant from within the current site (e.g. if you have a cross-site List View configured for the current site, or if you are using our Employee Portal or Self-service Portal which refers to lists in a different site).
Using "New Experience" will allow the form to be opened in the current (e.g. Portal) site vs bringing the user to the site where the list is actually created.
