When in standalone, any widget that takes a click event doesn't respond properly to user input.
Tested in 4.19(CL - 403788), 4.20(CL - 4228271), and 4.21(CL - 4229747)
Expected: The combobox should present the options provided.
Result: The combobox doesn't react to input.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-62154 in the post.