Are SAML + OIDC Cognito identity providers supported by Amplify on the web?

The Amplify Authentication docs for IOS outline support for the following types of identity federation:

• Facebook, Google, Apple here https://docs.amplify.aws/sdk/auth/federated-identities/q/platform/ios/
• SAML: https://docs.amplify.aws/sdk/auth/federated-identities/q/platform/ios/#saml-with-cognito-identity
• OIDC: https://docs.amplify.aws/sdk/auth/hosted-ui/q/platform/ios/

The Amplify Authentication docs for web browsers only outline federated identity support for Facebook, Google (+ Auth0) here: https://docs.amplify.aws/lib/auth/advanced/q/platform/js/

By digging into the Auth module codebase it's become apparent it's possible to invoke either a SAML/OIDC user pool iDP as follows:

Amplify.Auth.federatedSign({ customProvider: USER_POOL_IDENTITY_PROVIDER_NAME })

See: https://github.com/aws-amplify/amplify-js/blob/6c4d4b5fc737652f88dcdfa26bdb02a1defdfa2e/packages/auth/src/Auth.ts#L1924

Questions

1. Is this approach supported when using Amplify in a web browser? Looking purely at the docs would suggest it's not supported.
2. Amplify's PKCE support isn't documented anywhere. Similar question, it this something that will remain supported on web too?