When you use a SAML provider, you can configure a banner to be displayed at the login screen, PRIOR to login. For example, for Entra:
https://learn.microsoft.com/en-us/entra/fundamentals/how-to-customize-branding
This is done because many countries have either a law or case law that only makes it illegal to access a system if you tell the user BEFORE they login that they are not allowed to login.
It used to be common to display a banner post login, but it is not a good legal position to be in.