Nintendo releases a video highlighting the mysterious C button in the announcement on the day of the Switch 2 Direct. What is its function and how is it?

Nintendo releases a video highlighting the mysterious C button in the announcement on the day of the Switch 2 Direct. What is its function and how is it?
Nintendo released a video highlighting the mysterious C button in the announcement of Nintendo Switch 2 on the day of Nintendo. Attention is drawn to its features....

The linked article is in Japanese.