IdentityUI has a breaking change in .NET Core 3.0 11 September 2019 06:54 Sam MacDonald ASP.NET, .NET Core (0) TweetShareWith ASP.NET Core 3.0, Identity UI was moved to use the new static web assets introduced in this version. With this move there are some breaking changes to be aware of:.AddDefaultUI(UIFramework.Bootstrap4) no longer works.With the new change Bootstrap 4 is now the default UI Framework for use with Identity UI. If you are in need of using an older version of the framework then this can be done by using the IdentityUIFrameworkVersion property in your project file.The overload for AddIdentityUI that took a UIFramework parameter no longer exists in the latest versions of 3.0. If you are using Bootstrap 4, simply call AddIdentityUI(). If you need to use Bootstrap3, add the following line to your project file inside a PropertyGroup.<IdentityUIFrameworkVersion>Bootstrap3</IdentityUIFrameworkVersion>As I find more changes they will be posted here.