FreeBSD 13 definitely supports ConnectX-5 and ConnectX-4 NICs. But I can't find any information on the ConnectX-6 cards. They all use the same mlx5 drivers, so I would assume they are supported, as I see a tidbit here that FreeBSD had ConnectX-6 support since 2019: https://github.com/freebsd/freebsd-quarterly/blob/main/2019q1/mlx5.md (https://github.com/freebsd/freebsd-quarterly/blob/main/2019q1/mlx5.md)
Does anybody know for sure if OPNsense supports ConnectX-6 NICs?