Resource Capacity planning

It means that i can have a forecast view of my team work, in relation with the capacity, time

This is possible with defined planning.

-the ability to create and join a supply and demand forecast that highlights future resource gaps and surplus.

Yes, this is possible, for instance using some specific planninng mode tpo reserve availability for resources.

-flexibility of performing what-if scenario analysis to find the optimal solution set.

No, this is not possible.

-ability to create resource plans to resolve future resource imbalances.

Yes, but you must keep in mind that, opposit to MS-Project, ProjeQtOr planning never "over-loads" resources.
But you can see future "availability" of resources (periods when planning is not fuill for resource)

see team work capacity over a month for exemple

Reports => Planning => Colored monthly resource planning (you need to define a color on projects...)
Reports => Planning => Monthly planning Resource/Project (for detail day by day)
Reports => Planning => Work plan per month (for monthly work capacity)
Reports => Planning => Availability synthesis (to see left availability per month for each resource)

worked 1,5 work unit on somthing that he should have finished in just 1work unit, is it possible to have some kind of grapic to show that ?

Reports => Planning => Work synthesis per activity
Reports => Real work => Work synthesis per activity (same with somle smileys

you mean that it's possible to do custom planning ?

No, you cannot define "custom" planning manually.
But you can play with different planning modes.
For instance "regular between dates" can help you reserve some capacity to treat forcasted elements not received yet (for instance work on tickets that are not received yet)