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 ensure your system is making the most of the available services.
While the original Switch had no way of using LAN without an external device, the Switch OLED fixes this long-standing issue. One of the biggest improvements with the Switch OLED system is that the new Dock comes with a built-in Ethernet port. Having a built-in Ethernet port allows you to connect your console to LAN right from the get-go without needing to buy a separate device to make it work.
All you need to do is open the back panel, connect the Ethernet lead into the LAN port, and your internet will start running directly into the system while it’s docked. LAN internet is unavailable if your system isn’t docked.
Wi-Fi is always available if you want to play games in handheld mode without the Dock. But LAN is definitely the way to go if you’re playing a game like Super Smash Bros. Ultimate.