Switching workspaces has never been the hard part: the sidebar has a picker for that. Invitations were. One arrived by email, and the link in that email was the only way to accept it, so an invitation that went to spam or got deleted was effectively gone, and you had no way to check whether you had been invited at all.
There is now. Signing in lands on the Lobby, which has two tabs: the workspaces you belong to, each showing your role in it, and your pending invitations with a count on the tab. You can accept or decline an invitation right there, and a workspace you accept joins your list. The Lobby is reachable any time from the workspace name in the sidebar.
Memberships that have been disabled appear in the list too, labeled as disabled rather than quietly missing, so you can tell the difference between having lost access and never having had it.
Workspaces that sign in through your own identity provider send you there from the Lobby, so a mixed set of workspaces (some on SAML, some not) works from one list.
Everyone names their first workspace now
Signing up with Google was the one route that named your workspace for you. It built one automatically on your first sign-in, taken from your email address, which is how workspaces end up called after a company’s mail domain rather than anything a person chose. Signing up with an email address never did that: it sent you to a page to name one.
Both routes now do the same thing, in the Lobby: you name your first workspace yourself, and the separate page for it is gone.