How do I enable open registration in an account and allow instructors to add users to a course without Canvas accounts?
As an admin, you can enable Open Registration for your entire account. Open registration allows instructors with the appropriate permissions to add users to a course, even if the users don't already have Canvas accounts. When an instructor adds a user to a course, the user is sent a course invitation. To join the course, the user must first register with Canvas and create a password. The user's account will then display in the account Users list.
Even if Open Registration is disabled, admin roles with permission to add or remove users can always add users to courses without Canvas accounts.
Once this feature is enabled, instructors can add users in the course People page.