I didn't resolve this to my satisfaction. As I said, I was running an
Ubuntu 20.04 VM and consistently got the blank window. I found that when
I created a new Ubuntu 20.04 VM with no additional software loaded, I
did get the expected prompt for crede...
9 months later, Forticlient 7.0.0.0018 still seems to be the same
software with the same problem, still offered for Ubuntu 20.04 at
https://www.fortinet.com/support/product-downloads#vpn I tried 6.4.4 and
had the same problem. Maybe this is the same ...