In a WCP enabled setup, if the WCP clusters are not upgraded prior to ESX upgrade, then NSX is still pinned to the older version.
VCF 9.0 with WCP enabled
Incompatible WCP clusters with NSX version exist.
Upgrade the WCP clusters before upgrading NSX.
Prechecks will fail because NSX 9.0 requires minimum WCP Version to be 9.0.0.0.
https://docworks.broadcom.net/docworks-review/cms?type=AEM&documentIds=GUID-c2da0260-8bc5-436d-ad4b-af3f04b5a081-en&aemPubId=1215&reviewId=7489&topicToNavigate=GUID-8ce70ae0-fc52-4b0c-89fb-0246c604cbf1-en.dita