@mdubakov reinstalled our instance, and when I logged in, I see we had wiki and tasks by default.
I added project app, and as the little animated gif shows, I created a relation, tasks m:1 projects. I can see the link in the schema/domain diagram.
However, when I make a new board under a project, I cannot select tasks from configure board, cards. At first I did not have a task so I thought this was a problem but, adding a task to the project did not change this.
So far we restrict Types that are available in View setup with an App. In this case Projects App does not include Tasks, this is just a relation. So there are two options: