Illegal Characters in path
Which seem to be weird, or you even may dont understand that the cause of the above problem is the Model type being string.
Actually the reason that you get the above exception is that in your Controller you as usual called the View method passing the model as the only argument and the model value is a string. But what you may have not pay attention to is that View method also has another override which accepts an string as the view name. So if you pass the model like this code:
In the above code you specified to go to page with the name "myStringModel" and such a page does not exists. Solution: My suggestion is to select the right overload by specifying the argument explicitly, like the below code:
return View(model: "myStringModel");