Dear @Tony_Duke,
Also, anyone else reading the topic. We’ve added a Dialog API to SP forms. Now you can open another form in a dialog right from JS-editor like so: Dialog.open();
Please, check out our new documentation on how to open Plumsail Forms in Dialog mode, we hope you’ll find it useful - https://plumsail.com/docs/forms/javascript/dialog.html
Also, a blog article: https://medium.com/plumsail/forms-dialogs-d8df26f9984b
The solution through native Sharepoint API is deprecated in the new version. We’ve removed unnecessary dependencies to improve performance.
Tell us if you find anything unclear, or if you have any questions!