основываясь на этом, полагаю, что работала дискретная видеокарта, а не встроенная в intel

$ optirun -b none nvidia-settings -c :8

$ 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

Section "Device"
    Identifier "intelgpu0"
    Driver "intel"
    Option "VirtualHeads" "2"
EndSection

Section "ServerLayout"
    Identifier  "Layout0"
    Option      "AutoAddDevices" "true"
    Option      "AutoAddGPU" "false"
EndSection

Section "Device"
    Identifier  "DiscreteNvidia"
    Driver      "nvidia"
    VendorName  "NVIDIA Corporation"
    Option "ProbeAllGpus" "false"
    Option "NoLogo" "true"
    Option "AllowEmptyInitialConfiguration"
EndSection

Section "Screen"
    Identifier "Screen0"
    Device "DiscreteNVidia"
EndSection