So this is only for organizations and not for individuals? The Get Started button goes to a form where it wants to know how they can help your organization. I didn’t see any other link to the source code or documentation. If whoever created this site sees this comment, please clear up the above questions and observations.
I believe they're anticipating self-hosters to deploy directly from their Github documentation.
The FAQs in Github also imply that a hosted deployment for single users is on their roadmap, but not prioritized. - https://github.com/thunderbird/thunderbolt/blob/main/docs/fa...