Where is the Share option for test cases?
Looking at the documentation here for Zephyr scale: https://support.smartbear.com/zephyr-enterprise/docs/en/zephyr-enterprise/zephyr-user-guide/test-repository/sharing-test-cases.html Shows that ...
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The link you have provided is for Zephyr Enterprise, not Zephyr Scale.
You can still utilise the test cases from one project to another using Scale but only when adding test cases to a test cycle. I have added a picture but blocked out our company information. If you add a test case to a cycle the default project (top right of modal) is the project you are currently in, however you can change this to the project you wish to share tests cases from.
I hope this helps