Can I Just Show One Card at Showdown?

You can show just one card at showdown. However, showing just one will 7️⃣ not qualify you to win the hand even if that one card is revealed that you definitely have the best 7️⃣ hand.

At showdown there is no penalty in just flipping your cards up out of turn. However, most people like to 7️⃣ see what cards people acting before them have before deciding to show or not. If you are beat, you can 7️⃣ simply muck and not give away any information to your opponents.

Are the Showdown Rules Different Between Cash Games and Tournaments?

In 7️⃣ general, showdown is the same no matter what format you are playing. The only exception is that in cash games 7️⃣ a person may show one or both cards at any point during the hand without penalty.