I'd recommend reading "Inspired", specifically the two chapters on Product Roadmaps in Part III

Peter Yang's book Principles of Product Management covers this. The roadmap is a set of agreed plans and priorities - the word map is not super helpful here.

As remarked in other comments - once the objectives are agreed, the product roadmap can often crowdsource itself from other functions - engineering, design, etc.

Others already mentioned some about product roadmaps.

One great book I think almost any Agile PM should check out is "The Professional Product Owner" by Don McGreal and Ralph Jocham.

Essentially they take you through Agile Product Management.

Thanks for asking, cheers!

Jibran