Full Error Messages observed:
VCENTER upgrade bundle is not compatible with your existing version null. Refer to the https://knowledge.broadcom.com/external/article?legacyId=91728 to address incompatibilities and proceed with the upgrade. Please retry the upgrade once the upgrade is available again. Contact GSS for assistance, if the retry fails.
VCF 5.x
Per referenced KB VCF Future upgrade to 5.0+ blocked on the environment:
The environment may contain stale SDDC-M inventory, limiting the product to guide users with compatible future releases.
Verify products for compatibility. For additional assistance, please contact Broadcom Technical Support.