For a nutanix cluster to be able to install a newly released hypervisor, the information about it must be already in iso_whitelist file. This file can be downloaded from Nutanix portal (search for ESXi 6.7 U3) and is required when installing/upgrading hyperviosr using prism one-click.
ESXi 6.7 U3 (built number 14320388), has been out as of Aug, 20, 2019. It is Nutanix policy to support newly release hypervisors within 90 days after they are release by the hyperviosr vendors.
As of this writing (Nov 18, 2019), nutanix has released the iso file for this release and is supporting installation of this built on Nutanix clusters 5.10..6 and above.
Below is a public KB regarding the support for this release:
https://portal.nutanix.com/#/page/kbs/details?targetId=kA00e000000CsgLCAS