Hi,
Running Fortinet VPN successfully on a Snapdragon processor based device will require the 64-ARM version of the VPN client, it can be found here: https://www.fortinet.com/support/product-downloads
If you installed the default Windows Client, remove it and then check it there is a left over installer in the cache folder (the 7.4.x part might be different)
C:\ProgramData\Applications\Cache\{15C7B361-A0B2-4E79-93E0-868B5000BA3F}\7.4.3.1790\FortiClientVPN.msi
If the file is there remove the FortiClientVPN.msi before you attempt to install the 64-ARM version
Hope this helps,