Joan is compatible with Google Workspace accounts. This is not the same as your free Google email account. Rather, Google Workspace is an account associated with a domain that uses Google Workspace (mail, calendar, docs, and sites) for messaging and collaboration.
You can connect Joan with a free Google email account, however, please note that the personal calendar is not the same as room resources email. You can read more here.
To connect Joan with your free Google email account, please follow the instructions here.