It looks like I've found the problem which effects Windows 11 2H22.
If you are on a domain and manage group policies to each PC from the Domain, I found by accident that the group policies for Internet Explorer in the computer Configuration had stopped the service for FortiClient to running. I'm not sure which policy yet but I've managed to get the service working correctly. We have a couple of dozen policies so will take me a while to find the culprit.
Hope this helps those who have the same problem.