With the Spring '20 Release comes a potentially unwelcome surprise. The Closed picklist value for Case Status is defaulted to hidden. In this video I show you not only how to turn that back on, but other options for closing cases in Lightning, such as a Quick Action or using a Path.
Create a Close Case Quick Action Help Article - https://help.salesforce.com/articleView?id=cases_set_up_lex_close_case.htm&type=5
Adding a Path to Cases - YouTube Video https://youtu.be/BBsouPNeKIw