Attempting to upgrade to 4.9.1 from HCX Manager UI returns error message:
HCX 4.2.4 to HCX 4.4
Upgrading HCX Manager from all versions between 4.2.4 and 4.3.4 requires offline upgrade to 4.8.2 first.
Refer to Upgrade HCX Manager for Local Sites to download the HCX 4.8.2 Connector and HCX 4.8.2 Cloud Manager upgrade bundle and use the HCX Manager appliance management interface, https://hcx-ip-or-fqdn:9443, to perform the upgrade.
HCX upgrade bundle can be downloaded from the Broadcom Support Portal. Next to your profile on top right, click the dropdown and go to VMware Cloud Foundation -> My Downloads -> VMware HCX
Reference: https://knowledge.broadcom.com/external/article/142814/download-broadcom-products-and-software.html
Upgrade support for HCX versions past the End of General Support date will be provided on a best-effort basis.
HCX EoGS versions less than 4.2.4 are not qualified for upgrade and require full redeployment to the latest and supported build.