You shouldn't be calling
As the error message clearly states, you're writing a conditional in which one half is an
IHtmlString and the other half is a string.
That doesn't make sense, since the compiler doesn't know what type the entire expression should be.
There is never a reason to call
Html.Raw returns an
HtmlString instance that wraps the original string.
The Razor page output knows not to escape
HtmlString.ToString() just returns the original
string value again; it doesn't accomplish anything.