Searching for "FortiClient VPN 64 2021" typically refers to the 6.4 version of FortiClient, which was the active stable branch in 2021. Official Documentation (White Papers & Guides)
Why did companies standardize on this version in 2021? Because it introduced three game-changing features for 64-bit systems while still supporting legacy TLS 1.2. forticlient vpn 64 2021