Removed the server option to allow synchronous IO.

src/Umbraco.Web.BackOffice/Extensions/UmbracoBackOfficeServiceCollectionExtensions.cs

@@ -50,17 +50,6 @@ namespace Umbraco.Extensions
             //But as far as I can see, there are still precompiled views, even when this is activated, so maybe it is okay.
             services.AddControllersWithViews().AddRazorRuntimeCompilation();
 
-            // If using Kestrel: https://stackoverflow.com/a/55196057
-            services.Configure<KestrelServerOptions>(options =>
-            {
-                options.AllowSynchronousIO = true;
-            });
-
-            services.Configure<IISServerOptions>(options =>
-            {
-                options.AllowSynchronousIO = true;
-            });
-
             return services;
         }