Adding/Renewing/Replacing certificates from vCenter (Administration > Certificates > Certificate Management) would fail. One of the possible error is:-
Error occurred while adding trusted root certificates: Trusted root already existsVMware Cloud on AWS
In VMware Cloud on AWS, certificates related to management components like vCenter are renewed by Broadcom (Shared Responsibility Model Overview VMware Cloud on AWS)
Customers need not renew certificates of management components like vCenter in VMC on AWS. It would be renewed by Broadcom before the certificates expire.