Deprecated. This functionality now ships within Jetpack itself. See https://github.com/Automattic/jetpack/blob/trunk/projects/packages/connection/src/sso/class-force-2fa.php
When using a modern version of Jetpack, you only need to use the jetpack_force_2fa filter (docs). This will force 2FA for admin users (manage_options cap). You can modify this via the jetpack_force_2fa_cap filter (docs). Other filters are available.