It is not possible to login to the Steinberg Download Assistant and you may end up being refused or sent in a loop between Steinberg Download Assistant and the browser.
Two of the possible reasons are that either the Windows or macOS time is not accurate or there is an issue with the Internet connection that can lead to a time-out.
The first step would be to re-synchronize the system time to make sure it is correct and try again. There are several sources on how to do this, here are two external articles on the topic:
If this does not help, please use our regular download pages as a fallback solution. Most current applications are available as full installers there as well. For instance, the Cubase 11 downloads are available here.
We will further investigate the issue and improve the Steinberg Download Assistant as soon as possible!