Bugfix cannot parse StringValues as bool. Use ToString first.

src/Umbraco.Web.UI.NetCore/Umbraco/UmbracoBackOffice/Default.cshtml

@@ -17,7 +17,7 @@
 
 @{
     var isDebug = false;
-    var qryDebug = Context.Request.Query["umbDebug"].TryConvertTo<bool>();
+    var qryDebug = Context.Request.Query["umbDebug"].ToString().TryConvertTo<bool>();
     isDebug = qryDebug.Success && qryDebug.Result;
     var backOfficePath = globalSettings.GetBackOfficePath(hostingEnvironment);
 }