How to download the trial version of NSX for vsphere ?
There is no trial download for NSX.
You have to have bought it for the download to be enabled in MyVMware.
To trial/test it you have to use the HOL
https://my.vmware.com/en/web/vmware/evalcenter?p=vmware-nsx-hol
Try using the VMware Software Manager - https://my.vmware.com/en/web/vmware/info/slug/datacenter_cloud_infrastructure/vmware_software_manager/1_5
Then navigate All > Datacenter & Cloud Infrastructure > VMware vSphere > 6.5 > Any edition of vSphere, you will find VMware NSX from there.
when will 6.4 be available via the download service?