You can find detailed information on the enhancements and differences between EndNote 21 and previous versions here.
You can create and add tags with customized color and name to organize your references. For detailed steps, see here (Add tags).
*NOTE: It is important to note that while EndNote 20 and earlier versions can open and use an EndNote 21 library file, the tags associated with the file may not be displayed. However, these tags will be retained when the library file is opened with EndNote 21. In addition, using the Recover Library utility with EndNote 20 or earlier can lead to the removal of tags from the library.
With the new data restoration feature, you can easily recover your library from the cloud. You can also restore your entire library or specific references, compare and retrieve previous versions. Learn more here.
Cite While You Write (CWYW) add-on is compatible with Google Docs. You can insert EndNote references into Google Docs with CWYW tool. Refer detailed steps here for installation and use.
*NOTE: You will need an EndNote 21 Web account to log into CWYW in Google Docs. Register here if you do not have one.
The newly redesigned EndNote Web allows you to sync your library across your devices, from online, desktop, to iOS devices. It is exclusively available to EndNote 21 customers for 3 years, with unlimited storage for full-text documents, file attachments, and an unlimited number of references.
*NOTE: To enable sync from your EndNote 21: Click on Edit > Preferences> Sync > Enable Sync. Then click Sign up to login or to create an account.