I’m sorry to tell you that this is a wrong assumption. The Form package doesn’t come with any UI components (it doesn’t even contain any controllers).
The Form Builder is a “standalone” Flow package. It comes with it’s own UI and should be usable next to Neos but it is not an integration. See Flow Form Framework 5.0 Documentation — Flow Form Framework 5.0 documentation for more details.
The SimplyAdmire.Neos.FormBuilderBundle package was meant as integration but I don’t know whether it works with recent versions.
See Best capable Form-Builder for Neos for a related discussion