The following are the complete Nftables rulesets for both VPN gateways r1 and r2 in the example setup described in article Nftables - Netfilter and VPN/IPsec packet flow. The distinction between VPN and non-VPN traffic is done based on the peer subnet addresses.

root@r1:~# nft list ruleset
table ip nat {
        chain postrouting {
                type nat hook postrouting priority srcnat; policy accept;
                oif eth1 ip daddr 192.168.2.0/24 accept
                oif eth1 masquerade
        }
}
table ip filter {
        chain forward {
                type filter hook forward priority filter; policy drop;
                iif eth0 oif eth1 accept
                iif eth1 oif eth0 ct state established,related accept
                iif eth1 oif eth0 ip saddr 192.168.2.0/24 ct state new accept
        }
}

root@r2:~# nft list ruleset
table ip nat {
        chain postrouting {
                type nat hook postrouting priority srcnat; policy accept;
                oif eth1 ip daddr 192.168.1.0/24 accept
                oif eth1 masquerade
        }
}
table ip filter {
        chain forward {
                type filter hook forward priority filter; policy drop;
                iif eth0 oif r2 accept
                iif eth1 oif r2 ct state established,related accept
                iif eth1 oif r2 ip saddr 192.168.1.0/24 ct state new accept
        }
}