Since nftables is now the new default, a short note to myself on how to setup masquerading, like the usual NAT setup you use on a gateway.

nft add table nat
nft add chain nat postrouting { type nat hook postrouting priority 100 \; }
nft add rule nat postrouting ip saddr oif wlan0 masquerade

In this case the wlan0 is basically the "WAN" interface, because I use an old netbook as a wired to wireless network adapter.