How can I check which claims get sent from the SSO IdP?

If you want to see the claims like firstName | lastName | groups etc'...

You can use the Tenant SSO completed  log under Frontegg Portal ➜ [ENVIRONMENT] ➜ Backoffice ➜ Monitoring ➜ logs
Click on the log, and then click on the Raw Data tab.

Copy the SAMLResponse so you only have the value inside the quotes ""

You can paste it in this free online resource to decode the value-

https://www.samltool.com/decode.php

Then, optionally grab that result and past here to format the XML-

https://www.freeformatter.com/xml-formatter.html#before-output

This XML will contain all of the attributes and claims that were sent from the SSO IdP.