Once a project board is created, your very first task should be to link it to the portfolio. This will ensure the top-level portfolio of projects reflects the accurate summary status.
To do this there are two steps.
Link the existing task to the portfolio
On the project board you'll see a task called 'link existing and future...'. Against that task, click on the + symbol in the link to portfolio column.
(if you already have multiple tasks on your board, you will need to select all of them)
From the list that appears, search for and click on the task on the portfolio board that matches the name of your project
Then, link all future tasks to the portfolio
Having linked that task, we then need to link all futute tasks.
To do this, click the three dots on the board menu and select 'Default Item Values'
Then, in the link to portfolio option, repeat the process of searching for and selecting the task
Then you can mark that default task as 'DONE', your first one!