I have managed to create a couple of courses to experiment with. I have now deleted them. When I log in as administrator (on management.php) and search under my name, I can still see the courses which I thought I had deleted (including all the content of that course). I do not seem to find a place to delete them when logged in on the management.php page.
In your workspace logged in as your user (not via management) open the recycle bin and I suspect you’ll see the projects? You can then either delete them individually or select the recycle bin icon and then delete to empty the recycle bin and delete all the projects it contains.
They will then not show in management because they will have been permanently deleted.
HTH
Ron