It is possible to clone Zephyr test cases and test steps with Deep Clone for Jira.
Make sure to select the following options under “Advanced options”:
Clone issue properties → Clones test cases
Add clones issue link between clone and the original issue → Clones test steps
It is currently not possible to clone attachments that were added to Zephyr test steps. Attachments that were added to the issue itself can be cloned with Deep Clone for Jira.
The “clones” issue link can be removed manually after the clone is created. Due to technical reasons the link is needed initially when the test steps are cloned.