Hi Petr, not making excuses for the feature but a basic Planner plan doesn't have a concept of a timeline in it, like a premium plan does with a schedule. Basic plans have a series of dates, no formal start and end date like a project would in premium. It's basically a series of tasks with no 'interdependencies', no total % complete, which makes displaying data that's available in the Portfolio service, and related roadmap, difficult. The Portfolio feature as we understand it is really designed to display project schedules and their information ('a portfolio of projects').
It would be interesting to think through how a basic Planner plan with less structured work could related to a more formal project in premium, and determine a way to show them together.....