Its pretty simple this time around.
If you want to make the most of Nintendo’s shoddy online service to have a stable game of Super Smash Bros. Ultimate, then a LAN port is the way to go to make sure your system is making the most of the internet provided.
While the original Switch had no way of using LAN without an external device, thankfully, one of the biggest improvements with the Switch OLED system is that the new dock comes with an Ethernet port built into it so that you can connect your console to LAN right from the get-go without the need to buy any separate device to make it work.
All you need to do is open the back panel and connect the ethernet lead into the LAN port and your internet will start running directly into the system, so long as it’s docked. Obviously, you can’t use the LAN internet if your system isn’t docked and you are using it handheld, so just be aware of that.
You can, of course, still, use wifi if you want to play games that way. But LAN is definitely the way to go.