Can't Play Basic Online Games Because of Nat Type Issue

Don't know much of anything about networking, just know I can't play super Smash Brothers and other games on my Nintendo switch! I have the newest T-Mobile home internet router, the black rectangular one. Streaming content works just fine, browsing the internet works just fine, but gaming of pretty much any kind seems to be impossible, and I always get an error message stating that my Nat Type is incorrect or something of that nature. What can I do to fix this? I can create a hotspot on my phone and play Nintendo switch online just fine, surely I can do it with their advanced router.