Nintendo Switch error code 2618 0201?

I have the problem that I can't play online with the Nintendo Switch. The Internet works, the e-shop too, but something is probably blocked in the router that I can't connect to the other servers. I have a Fritzbox. In Mario Kart comes error code 2618 0201. In addition, the connection test Nat type F.

Or is it the speed? Download is 17 MB / s and upload 10Mb / s. Could it be because of that?

Does anyone know what you have to do there?

Try specifying the error code on the official Nintendo website. I did it once.

This is due to the internet connection. Try restarting the switch and the router too.