IRazorEngine razorEngine = new RazorEngine();
IRazorEngineCompiledTemplate template = razorEngine.Compile("Hello @Model.Name");
string result = template.Run(new
{
    Name = "<b>Test</b>"
});
Console.WriteLine(result);

RazorEngine razorEngine = new RazorEngine();
var razorEngineCompiledTemplate = razorEngine.Compile<HtmlSafeTemplate>(
    "<div title=\"@Model.FirstName\">This is now safe: @Model.FirstName</div>\n" +
    "<div>but not this: @Raw(Model.FirstName)</div>");
string result = razorEngineCompiledTemplate.Run(instance =>
{
    instance.Model = new AnonymousTypeWrapper(new
    {
        FirstName = "<script>alert(\"1\");</script>",
        LastName = "123"
    });
});
Console.WriteLine(result);

public class HtmlSafeTemplate : RazorEngineTemplateBase
{
    class RawContent
    {
        public object Value { get; set; }
        public RawContent(object value)
        {
            Value = value;
        }
    }
    public object Raw(object value)
    {
        return new RawContent(value);
    }
    public override void Write(object obj = null)
    {
        object value = obj is RawContent rawContent
            ? rawContent.Value
            : System.Web.HttpUtility.HtmlEncode(obj);
        base.Write(value);
    }
    public override void WriteAttributeValue(string prefix, int prefixOffset, object value, int valueOffset, int valueLength, bool isLiteral)
    {
        value = value is RawContent rawContent
            ? rawContent.Value
            : System.Web.HttpUtility.HtmlAttributeEncode(value?.ToString());
        base.WriteAttributeValue(prefix, prefixOffset, value, valueOffset, valueLength, isLiteral);
    }
}