Now sometime ago, on another threat I made, I came across a small discussion on whether the Rinnegan can be deactivated or not. To me it was obvious that yes it could, but I was presented with actually decent opinions on why it can't. So I will divide this into three parts: Proof that it can; Proof that it can't and How the idea of it not being deactivate comes from.
So point number one: Proof that it can: 1. Madara deactivated it. TWICE. Twice? I hear you asking. Didn't he only do once with Edo Tensei? Yes, and while that could be dismissed as being because of the Edo Tensei, the second time can't, as it was after Kaguya was defeated and Madara layed on the floor, dying.
But I've seen people saying that it's animation error. I doubt it but let's move on.
2.Sasuke deactivated it. What? When? You maybe asking. In The Last. On one scene (Obviously as he didn't have that many scenes there. AT ALL.) Now I ask myself how canon is The Last, but as I said on the other threat, Toneri appeared in Boruto, so I think I am good on this one.
3. It's a Dojutsu We've seen that no Dojutsu cannot be deactivated with the exception of the Rinne-Sharingan, which manifests on one's forehead so I don't see how that could be deactivated and Momoshiki's Rinnegan, which, again it's due to placement (This case forehead and palms).
4. It was never outright said it couldn't. Pretty self-explanatory.
Proof that it can't:
1. All Rinnegan User were never shown ACTUALLY deactivating. What? But you said it was. Yes yes calm down. I mean that we never actually saw anyone activating on-screen. Only off-screen. This lead many people to believe that they were Animation Errors, which I can see happening. (Except with The Last, that scene's lightning and over all look is way too good to be an error.)
2.During Boruto Sasuke is always shown with it. Pretty Self-Explanatory. But in my opinion that can be explained. He said (at least in the anime) that his Rinnegan was the only thing that could detect "Pieces of Kaguya" or some thing like that, I don't remember. So he could have it always active because he needs to be on high-alert so Kaguya doesn't happen again.
3. The Sage Of Six Paths was never shown without it after he awoken it. True, but just like Sasuke, he never needed to deactivate it. We know he has a huge amount of Chakra due to being the child of Kaguya so that was never a problem, but also so that he always looked powerful and had contrast to other members of the Otsutsuki Clan.
4.It was never outright said it could. Again, pretty self-explanatory.
Now time for the last point: How the idea that it couldn't came up:
1. Because the most we've seen of it came out of users that had it transplanted (Obito and Nagato), SPECIALLY NAGATO. And so people just dismissed it as so.
2. Same as points 3 and 2 of the "Why it can't" point. This is only a thing because people seriously dismiss those scenes I've pointed out in the 1st point and just treat it as animation errors or just forget them. Because they really weren't memorable.