Currently, it has no official document explain the differences between these two versions.
I just download both versions. It seems no special difference whether from the version number and user interface.
According to my understanding, the preview version could preview new features in advance; the insiders version includes the general available features.
If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.