Hello Xiaofei Ying,
DynamoCoreRuntime is a standalone sandbox version (Which means it’s own environment - when you unzip you can run the DynamoSandbox.exe file locally) of Dynamo Core - As shown in this blog post here: https://dynamobim.org/a-new-way-to-get-dynamo-sandbox/. Dynamo Sandbox does not sit on top of any other platform like Revit.
Dynamo 4 Revit is the Dynamo integration inside of Revit, and Dynamo 4 Revit version 2.1 is only available in Revit 2020 - As shown in this blog post here: https://dynamobim.org/dynamo-core-2-1-release/. Please note, as per the blog post, that Dynamo 2.1 is also available in other host integrations such as Civil3D, FormIt, Advanced Steel and Alias.