Hello, Kenneth, 

Please refer to the following help article demonstrating how to migrate to .NET Core: https://docs.telerik.com/devtools/winforms/core/core-migration

In case you have an existing application with .NET Framework 4.8 (or lower) you can use the newly released .NET Core Project Converter: https://docs.telerik.com/devtools/winforms/core/net-core-project-converter

The WinForms designer in .NET Core is still in its preview and currently it misses key features like support for user controls or libraries of third party vendors. We are closely working with Microsoft to determine the best possible implementation approach. At the moment we cannot provide you with a time estimate for a possible release or preview of the feature.

I can suggest referring the official Microsoft documentation for details on porting a project built on the full .NET framework to .NET Core: https://docs.microsoft.com/en-us/dotnet/core/porting/  Please bear in mind that the project file format in .NET Core is different so it will be necessary to update the old .csproj files. Microsoft have developed a tool to automate this process: https://github.com/dotnet/try-convert .

As for the designer, please note that even the Microsoft implementation is still limited and only available as a preview in Visual Studio. If you need to target .NET Core and have complex designers you may consider trying the workaround as explained here: https://github.com/dotnet/winforms/blob/master/Documentation/winforms-designer.md . With this approach you can still target .NET Core and at the same time achieve the design-time experience you are already used to.

Additionally, you can also check some of our resources on this topic:

https://docs.telerik.com/devtools/winforms/core/core-migration 
https://docs.telerik.com/devtools/winforms/core/deploy-application 
https://www.telerik.com/blogs/3-ways-to-deploy-a-winforms-or-wpf-net-core-application 

I hope this information helps. If you need any further assistance please don't hesitate to contact me.

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik