$ cat /etc/nftables.conf
flush ruleset

table inet filter {
        chain input {
                type filter hook input priority 0; policy accept;
        }
        chain forward {
                type filter hook forward priority 0; policy accept;
        }
        chain output {
                type filter hook output priority 0; policy accept;
        }
}

table ip nat {
        chain prerouting {
                type nat hook prerouting priority 0; policy accept;
        }
        chain postrouting {
                type nat hook postrouting priority 100; policy accept;
                oifname ppp0 counter masquerade
        }
}

2: enp6s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether e8:11:32:xx:xx:xx brd ff:ff:ff:ff:ff:ff
       valid_lft forever preferred_lft forever
3: wlp2s0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc noqueue master br0 state UP group default qlen 1000
    link/ether c0:f8:da:xx:xx:xx brd ff:ff:ff:ff:ff:ff
       valid_lft forever preferred_lft forever
4: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether c0:f8:da:xx:xx:xx brd ff:ff:ff:ff:ff:ff
    inet 192.168.x.1/24 brd 192.168.x.255 scope global br0
       valid_lft forever preferred_lft forever
5: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1492 qdisc fq_codel state UNKNOWN group default qlen 3
    link/ppp 
    inet xx.xx.xx.xx peer xx.xx.xx.xx/32 scope global ppp0
       valid_lft forever preferred_lft forever

$ sudo iptables-save 
*nat
:PREROUTING ACCEPT [27871:3027274]
:INPUT ACCEPT [27418:2991500]
:OUTPUT ACCEPT [48491:3681377]
:POSTROUTING ACCEPT [1115:67462]
-A POSTROUTING -o ppp0 -j MASQUERADE
COMMIT
*filter
:INPUT ACCEPT [7441829:404174002]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [14280656:20766836283]
-A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -i br0 -o ppp0 -j ACCEPT
COMMIT