I want to share my wifi internet with lan cable to a raspberry pi, but it seems network manager doesn’t respond to the dhcp requests. When I see processes listening on 67/udp only a dnsmasq process is listening, and I guess it prevents network manager from doing the dhcp work. But I don’t have dnsmasq in my nixos config and I don’t know where it comes from. The other thing worth to mention is that I was able to share my internet using network manager before nixos 23.11.
dnsmasq is started by NetworkManager to provide a dhcp service.
It might be useful to run nmcli to get the status of all networks.
I seem to have a similar problem: I do see networkmanager start adnsmasq process (with --conf-file=/dev/null 
), and I do see the client sending DHCP Discover request, but dnsmasq does not appear to be responding to them.
Ah, I needed to open up port 67 in the UDP firewall. Added this to Internet Connection Sharing - NixOS Wiki