Well to some extent I trust projects that have an active telegram group that always respond to it's members and answers their questions.But it is not an assurance some successful project do not have an active telegram group while some scams have a very active group so the best thing is just to have adequate knowledge about a project before making an investment.
You don't need to pay attention to the activity of the project group in the telegram channel at all. Spend more time studying the main papers of the project and its team.