The accessPackageAssignments endpoint does not support filtering on catalogId. For example: https://graph.microsoft.com/beta/identityGovernance/entitlementManagement/accessPackageAssignments?$filter=catalogId eq '{catalog-guid}'
Would be useful for users with limited access to Entitlement Management who want to see all of their active user assignments in a single API call. Otherwise they're forced to loop through all of their accessPackageIds and query the assignments one package at a time.
https://graph.microsoft.com/beta/identityGovernance/entitlementManagement/accessPackageAssignments returns a 403 for users who only have access to a limited set of Catalogs.