can a test case be executed without a test step?
You need to create at least one test step for a test case to be executed manually (through the test execution screen).
I would vote for adding this capability because I also use Spira as the system of record for checklists; I do not use it exclusively for managing test scripts. This is especially useful when you want the testers to use exploratory testing and not necessarily follow an explicit script; yet you still want to show coverage against requirements.
Requiring at least one step feels bulky when setting this up, although it is workable. We standardized on using the first step to outline the input conditions that were not already obvious from the title of the test case.
The other reason I would vote for this is that other test management systems have this capability.