Welcome to vmware community.
In order to install VCSA 6.7U3 from Mac Catalina workstation you have to download the "VMware-VCSA-all-version_number-build_number.iso" from the VMware Web site at https://my.vmware.com/web/vmware/downloads.
Confirm that the md5sum is correct.
See the VMware Web site topic Using MD5 Checksums at http://www.vmware.com/download/md5.html.
Mount or extract the ISO image to the client machine from which you want to deploy the appliance.
Note: For Mac OS, you can use DiskImageMounter.
You can refer to the below doc for more details:
Yes, I know how it should work. I've installed or upgraded many vCenters many dozens of times from my Mac workstation.
I'm saying Catalina is _different_ due to Apple's increased security profile.
I can take the same ISO for the vCenter 6.7U3 installer on an older Mac workstation, and install it fine.
Using the same ISO mounted on two different Catalina Mac computers, I have problems. The first two problem seem to be able to get around. The one with the libraries not being from a trusted vendor put a stop in my ability to do this from Catalina.
And of course, it works fine from a windows workstation.