When an auth method is disabled all users authenticated via that method lose access.

The statement is true. When an auth method is disabled, all users authenticated via that method lose access. This is because the tokens issued by the auth method are automatically revoked when the auth method is disabled. This prevents the users from performing any operation in Vault using the revoked tokens. To regain access, the users have to authenticate again using a different auth method that is enabled and has the appropriate policies attached. References: Auth Methods | Vault | HashiCorp Developer, auth disable - Command | Vault | HashiCorp Developer