What is the difference btw AWS active directory services VS cognito identity pool VS SAML VS IDP's?

Hello.

AWS Directory Services is used when using Active Directory on AWS or when linking with an existing Active Directory on-premises.
For example, you often use AWS Directory Services when joining an RDS MSSQL server to Active Directory or using an FSx Windows file server.
https://docs.aws.amazon.com/directoryservice/latest/admin-guide/what_is.html

Cognito identity pools are used to grant temporary AWS credentials to authenticated users.
For example, suppose an application user wants to access S3.
By setting up an ID pool at that time, it is possible to give access rights to S3 from application users.
https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-identity.html

It is not a service as it is a standard for authentication information used for SSO (single sign-on) and ID linkage.
https://www.onelogin.com/learn/saml

OIDC is an authentication protocol that extends OAuth 2.0.
https://www.microsoft.com/en-us/security/business/security-101/what-is-openid-connect-oidc

The following document contains a comparison between SAML and OIDC, which I think will be helpful.
https://auth0.com/intro-to-iam/saml-vs-openid-connect-oidc

IdP is a service that stores, manages, and provides user authentication information.
https://www.cloudflare.com/learning/access-management/what-is-an-identity-provider/