Since updating my FortiGate to 7.2 firmware, I noticed that my Remote Desktop resolution was forced to 1024×768 when previously it was able to use dynamic resolution based on the browser window size.
This was apparently a change that was forced in the 7.2 updates and ignores the setting you will have configured as a bookmark in the SSL VPN Web Portal.
Solution
This requires some CLI to resolve the issue but luckily will help apply to all users.
You will need to configure the Default Window size for EACH Web Portal you have configure that is using RDP connections.
config vpn ssl web portal edit "<web portal name>" set default-window-width 0 set default-window-height 0 next end
Make sure that any bookmarks are also set to have their width & height set to 0, but I’m assuming here that this was already the case.