For you to join a Team on Vercel, one of its owners can invite you from the Team Settings on the dashboard (or, in the case of SAML, add you to the respective Directory Sync provider).
In addition, the platform now also suggests Teams that you can request access to based on:
The Git namespaces (e.g. GitHub organizations) that any Git Login Connections associated with your Personal Account have access to.
The email domain associated with your Personal Account.
Suggested Teams will appear on a new Teams page in your Personal Account Settings (which also provides an overview of the Teams that you're already a part of) and in the scope selector on the top left of the dashboard.
Check out the documentation as well.