Did either of you need to forward your ports before to play each other Steam-to-Steam? If so, then you’ll have to change the port forwarding to the Switch instead of the PC. The ports that may need to be forwarded are at this link: Ports to forward for connection issues: UDP 9991 and 19900
I can speak from experience and say: yeah, sometimes you need to forward your ports. I had to forward my ports on the Steam version and the Switch version didn’t work for me until I changed my port forwarding settings to go to the Switch instead of my computer
There is currently a bug with the animations during online play on the Switch. A hotfix will be released as soon as Nintendo pushes it out. The fix is out on the PC and PS4 version, currently. The animation bug is what is making it seem like it’s way laggier.