When you want to launch Form Publisher, you get an error message saying that Google Drive refused to connect. This article explains how to solve this issue.
This issue is not directly related to the Form Publisher add-on but to a Google outage.
First, make sure you are not logged in with multiple accounts. Learn more: How to log out from multiple accounts?
If you still have the issue, log out from your Google account. Then log in again and start to use Form Publisher.
To learn more about how to troubleshoot this issue, you can also read Google documentation.