As of the release of Catalina, App Notarization is strictly enforced on macOS. Apps not notarized will not be installed or opened. This includes certain builds of Ignition and its various launchers (Vision Client, Designer, and Perspective Workstation).
The warning is due the operating system not recognizing the installer. Should you run into this scenario, you can work around it by temporarily disabling the validity check.
You can by pass this by running the following from Terminal
sudo spctl --master-disable
Once disabled, run the installer by right clicking on the
.app, and selecting "Open". After installation is finished, you can re-enable the check with the following Terminal command:
sudo spctl --master-enable