Take it from the bottom up:

Step 1: look at ip link show on both sides. If they have NO_CARRIER, check your cable.

Step 2: Look at ip address show on both sides. Do they both have one? Do the subnets and masks match?

Step 2a: Is the client side configured to be up and ask for a DHCP address? Is Dnsmasq actually running on the server side? is it listening in the right interface?

Step 2b: use tcpdump -ttt -e -i eth0 on both sides to watch for packets. Do you see DHCP or bootp requests coming from the client? do you see responses coming from the server?

Step 3: Look at ip route show in the client. Is the default route correct? Is it the router’s IP? Can you ping the default route? Is DNS configured and working?

Step 4: look at your nftables. do you have NAT set up right? look at tcpdump on the client and both sides of the router. when the client tries to get to the internet, do you see packets go all the way out and all the way back?

This (multi-monitor support) is exactly why I switched to sway from i3wm, and haven’t looked back.

Not a gamer, so I can’t speak to that aspect, but for everything I do there’s not much difference.