The simplest solution I inadvertently stumbled into after trying different ways suggested by other users...was to simply uninstall Forticlient ( I had version 6.4.xxx on Big Sur) completely from my comp. There's an uninstaller that I had downloaded from Fortinet website many years ago (still works) that does a clean job. Can't find it now though, lucky I still had it. Or just follow the usual process of completely uninstalling the Forticlient app from your Mac on Monterey.
Make sure to take a screenshot of the VPN settings and keep it safe before uninstalling.
Then use the normal Forticlient (VPN only) free software downloaded from Forticlient's website (latest version 7.2.xxxx). Double click and follow through the process/steps as prompted. Set up the VPN from the screenshot u took earlier and it starts working. No problems at all.
No need for using complex terminal commands and searching for the installer in temporary files