The NSX upgrade fails during the precheck stage due to expired certificates on the NSX Manager, and the same behavior is observed even when the upgrade is initiated from the SDDC.
The failure occurs during the certificate validation precheck on the NSX Manager UI, resulting in the following error:
The certificate with id #.#.#.#.#.#.#.# failed to parse with error: null please delete (if unused) or replace this certificate prior to upgrading.
If the upgrade is initiated from the SDDC, the verification can be done by reviewing the LCM logs on the SDDC Manager: /var/log/vmware/vcf/lcm/lcm.log
VMware NSX
This is expected behavior, as the precheck validation fails due to the expiration of the NSX manager certificate.
Generated the new certificate and replace the expired certificate using API call as per the document below and rerun the prechecks: