Can cards with exhaust effects be used during an opponent's turn or during showdown phase?

Ruling: Exhaust abilities can only be used during your turn when there is no showdown or chain active, unless they have an Action or Reaction tag.

Nuances:

• Abilities with the Action tag can be used during showdown
• Abilities with the Reaction tag can be used in response to triggers
• Without these tags, exhaust abilities are restricted to your turn outside of showdown/chain