Only users that have Telerik installation version 2021.1.122 are affected.
Clients that have Telerik installation version 2021.1.122 can not build successfully .NET Core/.NET 5.0 projects. The following error occurs while compiling the project:
The problem is a missing NuGet fallback folder.
You should create the missing ToolboxNuGetPackages folder in the installation folder of the controls, usually at C:\Program Files (x86)\Progress\ToolboxNuGetPackages.