https://www.gamespot.com/articles/e3-2018-fortnite-for-switch-has-cross-play-with-xb/1100-6459769/

Fortnite launched for Nintendo Switch today, and now we've learned a little more about its features. The game supports cross-play with the Xbox One, PC, and mobile versions, Epic's Nick Chester confirmed on Twitter following the game's announcement at Nintendo's E3 2018 briefing.

The only major platform left out of the cross-play action is PlayStation 4. This is likely due to Microsoft and Sony not being able to come to terms on a cross-play deal.