How can I open a new window from a form?

Option 1. Using the Open URL Image Button (while in a form), have the option to open in a new tab enabled. After that, create an Active Form Flow to pass in the Dynamic URL link.
Option 2. Another option you could use is the End Form Session step, and select Open URL, then provide the URL you want under Inputs in the Properties Panel.

Useful Documentation:

[url=https://documentation.decisions.com/projects/docs/opening-a-form-in-a-new-window?highlight=open url]https://documentation.decisions.com/projects/docs/opening-a-form-in-a-new-window?highlight=open url[/url]

[url=https://documentation.decisions.com/projects/docs/using-end-form-session-to-navigate-pages?highlight=end form session]https://documentation.decisions.com/projects/docs/using-end-form-session-to-navigate-pages?highlight=end form session[/url]