I’m not entirely sure what’s causing the problem, but I’d start by inspecting the values you feed into SetSelectedOption — it’s possible your ToText node is adding extra whitespace or formatting.
As a cleaner alternative, you could store your resolutions in an array of FIntPoint instead of converting them to text. That way you avoid any string-parsing issues and keep your logic type-safe.
If you need more fine-grained control over window sizing (for example, distinguishing between viewport size and game resolution), this thread has a good explanation and some code samples:
How to get current screen size/resolution? - Development / Programming & Scripting - Epic Developer Community Forums