Closed projects don’t show in the main projects kanban view.
The “Closed” kanban column is there so you can drag and drop projects to close them but you can’t see all previously closed projects in this column.
The reason for this is because once you have many closed projects this would result in the “Closed” column becoming very long and hard to use.
Closed projects can be seen on the projects list view page. It’s not an issue to show projects on the list view page as it is paginated so you can navigate through 20 projects at a time on each page.
You can filter the list view to see only “Closed” projects if you like. This may help you see the closed projects only or drill down to the specific projects you want to see. To do this use the filter button at the top right of the main project list view page.