VCF Operations, SDDC Manager and the other VCF Management components have already been upgraded to 9.1.
Management domain vCenter and NSX are still on 9.0, VCF is in a mixed-version state.
The user is unable to configure "Fleet Settings" under Manage > Fleet Management > Fleet Setting, VCF Operations shows "VCF License Required":
VMware Cloud Foundation 9.1
As VCF Ops Components are already on VCF 9.1 but vCenter still is on 9.0.2, the mixed-version state is causing this issue due to architectural shift in VCF 9.1, VCF Operations is unable to fully validate the VCF 9.1 licensing state or bind to the new Fleet Settings framework until the legacy components are replaced and upgraded.
Please upgrade vCenter in the Management domain to version 9.1. Afterwards the Fleet Settings in VCF Operations should be fully functional: