use setActive(true/false); with GameObject.FindGameObjectsWithTag

I am trying to use GameObject.FindGameObjectsWithTag to create a set of game objects that I can turn of or on. If I leave as a game object-
private GameObject turnOffCards;
it returns Cannot implicitly convert type UnityEngine.GameObject[]' to UnityEngine.GameObject’

if I call it an array
private GameObject turnOffCards;
it returns
Type UnityEngine.GameObject[]' does not contain a definition for SetActive’

What should I use?
Many Thanks!

That’s because you’re trying to SetActive() an array, which isn’t possible. You need to loop through the array members and do it for each.

for(int i=0;i<turnOffCards.Length;i++)