Hi @Simon_Barnes - Thanks for the question. Welcome to the community.
There are 2 possible flows :
Identity Provider Initiated (IdP-initiated) SSO
User logs into the IDP Portal
Quick Sight application is configured
User is redirected to Quick Sight homepage when clicked .
Service Provider Initiated (SP-initiated) SSO
Quick Sight can also be configured for SP-initiated sign-on in the Enterprise edition. This setup enables Quick Sight to redirect the user to authenticate with the IdP first before granting access to the Quick Sight resources.
If Identity Provider Initiated (IdP-initiated) SSO > You can have users from multiple IDP’s logging into 1 Quick Sight account.
If Service Provider Initiated (SP-initiated) SSO > It is indirectly possible to configure multiple SSO provider via intermediate dummy application landing page. Quick Sight SSO configuration can be pointing to this dummy application page. This dummy page can have redirection code-logic to point to correct IDPs. (E.g. this dummy application page will redirect to appropriate IDP, authenticate based on user-attributes like emailID/username and relay user back to Quick Sight on successful login).
This blog walks through the steps to map three identity sources with identity center.