In the previous version of JIRA, it was easy enough to create a board in an existing project. You could do it from the project, or you could also go to the "boards" tab in the main nav. However, if I do not already have a board, there is no way to create a new board in the new JIRA UI.
Funny enough, if you do have a board in your project, you can create another by clicking on the three dots in the project's board view.
It makes it difficult to set up a new project, because I now have to create from Scrum or Kanban, and go back and set up the all schemes I need. I would much prefer to copy from an old project structure, and only have to set up the board.