Hi Weilies Chok,
You can try enabling roadmap feature by opening project setting and select feature. This may help bring back the 'roadmap' link for existing project.
Or you can try Agile User Story Map & Roadmap plugin. I'm using this to create roadmap and manage product because of a wider variety of features such as story map, user's persona, clear backlog, planning sub-task. It's quite cheap and free for the first month.
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