I run to this very strange issue, where in the VAMI options to stage or install update are greyed-out. I have a case opened with VMware, however taking in to the account security advisory I decided to run update from ISO.
Here is the Runlist:
- Download ISO form Vmware website
NOTE: you will need to login

- Upload ISO to datastore.
NOTE: if you receive error message during upload or upload will not strat, more likely it is related to certificate. Download and install root certs from vCenter welcome page

- SSH to your VC
- Make sure that you are in appliance shell (NOT BASH)
- Run this comand:
software-packages stage --iso
- You can verify upgrade packages by running this command:
software-packages list --staged
- Run update:
software-packages install --staged
8. Be patient it will take some time! Job done!
Here is a video for step-by-step instruction:
If you need explanation or you do have any questions related to this script, please do not hesitate to leave the comment.
Visit my FB page: https://www.facebook.com/AngrySysOps
Subscribe to my YouTube channel: https://www.youtube.com/channel/UCRTcKGl0neismSRpDMK_M4A