In the AWS console, the management account of an organization can deactivate Reserved Instance discount and Savings Plans discount sharing for any accounts in that organization, including the management account. This means that Reserved Instances and Savings Plans discounts aren't shared between any accounts that have deactivated sharing.
https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/ri-turn-off.html
Does Partner Generated Billing (PGB) detect that the Reserved Instance (RI) and Savings Plans (SP) sharing setting is deactivated?
Partner Generated Billing does not detect whether a linked account has RI/SP discount sharing activated or deactivated. We apply the discounts to the linked account even if they have RI/SP discount sharing deactivated.