The option to submit an assignment after a due date may be determined by your instructor, institution guidelines, etc. In this case, if the due date and/or the late due date has passed and you want to submit, please reach out to your instructor directly (as they may be able to submit on your behalf).
Some Gradescope assignments have late due dates set by your instructor and allow submissions after the due date has passed. The following is an example of an assignment that accepts submissions after a due date. On the assignments dashboard, you will see an Accepting late submissions message in the Released column for an assignment, which indicates that you can submit to it after the due date has passed. Additionally, if a due date has passed and you can no longer submit to the assignment, the assignment name will not be selectable. For an example, see the reading quiz assignment name in the image below and notice that it is greyed out.