Officially, Kingdom Two Crowns is not a free-to-play game. However, developers frequently offer opportunities to experience it at no cost:
Occasionally, the game has been offered for free on iOS for short promotional periods. What’s New in Patch v1.1.16? Kingdom Two Crowns Free Download (v1.1.16)
The game often has Free Weekend events on Steam and Xbox, allowing you to play the full version for a limited time. Officially, Kingdom Two Crowns is not a free-to-play game