Handle the msbuild copy in two steps, so we can override the wwwroot/umbraco folder from outside, using the following in the project csproj.

<PropertyGroup>
        <UmbracoWwwrootName>my-secret-loginpanel</UmbracoWwwrootName>
    </PropertyGroup>

    it will now copy to wwwroot/my-secret-loginpanel instead of wwwroot/umbraco

src/Umbraco.Web.BackOffice/Install/InstallController.cs

@@ -93,7 +93,7 @@ namespace Umbraco.Cms.Web.BackOffice.Install
 
             await _installHelper.SetInstallStatusAsync(false, "");
 
-            return View(Path.Combine(baseFolder , Cms.Core.Constants.Web.Mvc.InstallArea, nameof(Index) + ".cshtml"));
+            return View(Path.Combine(Constants.SystemDirectories.Umbraco.TrimStart("~") , Cms.Core.Constants.Web.Mvc.InstallArea, nameof(Index) + ".cshtml"));
         }
 
         /// <summary>