Recently I did the Catalina Upgrade to both of my MacBook Pros. FortiClient was working on both. Then on ONE of them, I did the supplemental patch. That patch killed my FortiClient. Man was I on fire. Fortinet announced that 6.2.2 would fix the Catalina problem. I attempted to uninstall FortiClient on my laptop but continuously got the FortiClient screen but everything was grayed out. Needless to say I was not a happy camper. Since Apple does not give you information about what they did with their patches, there was no way for me to figure out what I could do to reverse the issue.
I attempted to use the uninstaller but would get and error message to the affect of "Forticlient is running, please shut it down". So I decided to manually remove it via the CLI. I was unable to uninstall or re-install over top of it. Here is what I did.
Shell out to a terminal window. Use the Terminal or iTerm2 or whatever floats your boat.
sudo rm -rf com.fortinet.forticlient.*
cd "Library/Application Support/Fortinet"
sudo rm -R FortiClient
Reboot the Mac
run FortiClientUninstaller from the Applications Folder
You should now be able to re-install FortiClient