Civilization VI gets a massive patch this week which includes major rebalances to the civs, in particular for the new Gathering Storm expansion. But out of those long changes, which you can peruse here, there is also another feature being added: cross-save.
If you have the Nintendo Switch version and the Steam version of the game, you can transfer the same saves over either platforms. Though you will need to have a 2K account to make use of the cross-save feature.
Civilization VI now supports cross-platform cloud saves on Steam and #NintendoSwitch. Link your @2K Account, tick the multi-platform cloud save box in options, and you're good to go!
Get your 2K Account: https://t.co/HX0bxwgmnt pic.twitter.com/LxYdxG7hbp
— Civilization VI: Gathering Storm (@CivGame) April 2, 2019
Also, the Switch version has yet to see any of the two expansions, so cross-saves only work for vanilla Civ VI at the moment.