If there are any issues and you don't know why something doesn't work - we'll have to take a closer look: we'll need screenshots with form URLs, group membership and conditions that you use.
As an Admin/Owner/Designer, I am in every group, thus prohibiting me from "Excluding the selected groups". Once I removed exclusions, the form routed as desired. Now - I need to figure out how to exclude all other but a few of us who will be using the +New form.
I was getting hung up on JS code editor and/or the Custom Routing editor.
By selecting the groups you are restricting access to the form set. E.g. if you choose the Site Owners group, only users in this group can be redirected to this form set.
In your case, you can create a new group and add to it only users that should be able to open this form set and choose this group in the From Set settings