Greetings, Atlassian team members!
The Jira Product Discovery (JPD) team and Atlassian provide a Product Management Handbook as a resource:
https://support.atlassian.com/jira-product-discovery/docs/the-product-management-handbook/
Why can this not be downloaded with a Gmail email address as a contact?
Until recently, this same problem existed for signing up for Atlassian-sponsored webinars...which was made more visible by the community adding combined / linked accounts, with one as a primary to prevent loss of content / history access. And so people using a Gmail account as a primary could not use such resources.
Kind regards,
Bill