Your courses typically stay in Blackboard for one year and one week past the semester when you took them, and they will not be deleted.
However: you can choose not to view courses you're no longer taking! Here's how:
In your Courses area, look up at the top. In the center, you'll see a label that shows you which courses you are currently viewing.
When you click on the chevron next to the one in the center, you can choose which courses to view. In this case, I want to view my Spring 2023 courses, so that's what I'll choose from the menu.
Now, in the Courses area, I will see only my Spring 2023 course(s):
If you ever decide that you want to see a course you took previously, you can instead select a previous semester.