I'm not that familiar with newer c# code and only recently started with result pattern but tbh, I can't tell what is this code supposed to do. Does opt resolve to true or false in this case? Why do you want TestStringFail to always execute, and what should it return? Why is opt.None true when it was initialized with a valid string value, what does None even mean in this context?
The operator being applied to the ResultObject will always resolve to the Generic type that was specified as 'T in IResult<T>. If the function is not successful the resolved value will be whatever value was supplied to the ResultObject constructor, the opt.None property will true and the opt.Some property will be false.