Impact/Risks:
The customer would not be able to link M18 SDDC with an M20v1/M20v2 SDDC.
To understand why this issue occurs and the next plan of action.
The error, "Link from VC: "FQDN of VC 1" to VC: "FQDN of VC2" failed : [{args=[], default_message=Error during link: java.lang.Exception: Failed to copy any Cert, id=community.error.runtime}]" is encountered when attempting to link an M18 SDDC with an M20v2 SDDC via SDDC Group's vCenter Linking feature.
This is caused by an incompatibility of the cryptographic algorithm, M18 SDDCs use SHA-1 algorithm compared with the SHA-2 algorithm that has been implemented starting with M20+.
Create a VMC Support Request (Creating and managing Broadcom support cases) with a screenshot of the error and business impact.