and welcome to the forums.
The FortiClient offers IPsec VPN and SSL VPN, not L2TP. You can use the built-in L2TP VPN in Windows if you like but most people would recommend to create an IPsec VPN for remote access. You can use FSSO with both IPsec and SSL VPN.
OK, this can be confusing because in L2TP VPN there's IPsec mentioned as well. The underlying protocol is L2TP but some part of the data is encrypted by IPsec. FortiClient does not support L2TP protocol.
post edited by ede_pfau - 2018/02/08 11:53:46