Nintendo has been kind enough to drop a Captain Toad: Treasure Tracker demo onto the eShop. Now, unfortunately it’s only available on the Japanese eShop, but it’s not that hard to create an account to access the Japanese eShop. You can then use your own account to play through the demo in full english.
The demo is 204 MB to download. There’s three levels to play, two regular levels and a boss battle. The demo also supports two players and touch controls.
We have created a guide that tells you how to access the eShop from other regions on your Nintendo Switch. You can find that HERE.