Thanks for sharing the screenshot and your workaround, which I think is a good solution considering the limitations of interacting with spinners/drop-downs.
Out of curiosity, from your screenshot of the “All Objects” tree, it looks like there are 2 TextViews within the Spinner->LinearLayout hierarchy. If you inspect those TextViews, what do they show?
Finally, I’ve been working on an open source library that you can use in your Katalon testing projects. It provides some convenience methods for working with things like drop-down menus. It might be of some help to you, specifically this part: https://github.com/detroit-labs/katalon-mobile-util#using-a-textfield-with-a-picker-list
For info on how to include third party libraries into your tests, you can see the Katalon docs: