Check out the things that you need to do to connect your classic Nintendo Switch to the router with an Ethernet cable in this article. Fix #9: Contact Nintendo support.

Wired (LAN) The second way to connect to the internet with a Switch 2 is by connecting it directly to your router using an Ethernet cable.

How to Connect Two D-Link Routers. As you get more and more Internet-enabled devices, what once seemed like plenty of Ethernet ports on your D-Link router may no longer be sufficient. One option ...

Of course, the better solution would be to connect an Ethernet cable between your router and your switch. If you can't do that for some reason, get a wireless bridge and plug it into your switch.

If you have a dual-band Wi-Fi router, switch it from 2.4GHz to 5GHz if available. The Nintendo Switch supports both, and the faster band might help fix any internet or Wi-Fi connection issues.

The switch to router Ethernet cable had Cat 5e written on it, but in the router interface, the link said it was autonegotiated at 100Mbps. Changed the cable, and now everything is peachy.