How to create a new request on roadmap portal?
Eventually, the items that are displayed on the roadmap portal are Jira service desk tickets. So whichever way these tickets are created, depending on the configured JQLs on columns they will be or won’t be displayed.
JSD widget can also be inserted within the roadmap portal as explained here https://amoeboids.atlassian.net/wiki/spaces/RPJSD/pages/1553760295/How+to+manage+a+roadmap+board#Using-JSD-widget
Or simply add an additional link at the top that points to the service desk customer portal, where tickets can be created.