I don't think readers notice 3rd person view as another character observing the MC.
I have read many books written in 3PL (3rd person limited; narrator only knows the thoughts and feelings of the MC, everything else is seen through the MC POV), and I recall scenes of masturbation, or celebration when alone and something great happens, or grief in solo, etc. I never lose my reading reverie and think "somebody is watching this girl crying alone in her room!" or anything close to that.
There are many things that do break my reading reverie, but that isn't one of them. I will tell you what one is though: Somebody that is supposed to be going through extreme trauma, physical pain or betrayal or confusion, being drugged or poisoned -- yet is strangely articulate and descriptive of their own chaotic state of mind, feelings, the situation, etc. That does not feel realistic.
Because of that, I recommend 3PL, it offers more flexibility. The narrator can describe how the MC feels when the MC would not plausibly be able to do so.
We similarly don't mind the narrator describing settings and scenes in detail that it just isn't plausible for the MC to do in thoughts or impressions; because whatever the MC thinks, in images or words, takes time in-story. But the reader gets the sense that the narrator is exempt from time and outside of it, when it comes to descriptions of setting and scene, or description of characters or devices.
The narrator can tell us, at length, about what the MC already knows without the MC having to consciously review what she already knows. Also about what the MC has experienced without the MC having to consciously review it. It doesn't read like an authentic thought to say I trained six years in Wing Tsun Kung Fu, at my father's insistence, always afraid I'd be raped, like his sister.
But it is fine if the narrator mentions something like that, and relates a paragraph about it, to provide details about what the MC already knows and experienced, so the reader is not blind-sided when the MC defeats two armed muggers in a few seconds, leaving them incapacitated in an alley. To me, it is far more difficult for a first-person narrator to do anything similar without it sounding awkward and unrealistic.
This is particularly true in skills the MC may have, like the martial arts example. In situations where we (humans) apply our skills, we don't think about the history or learning of them, we just do things. The whole point of martial arts training (particularly in the martial arts) is to build the moves and reactions into muscle memory, so we don't have to think about it, we just do it. Other skills, like typing, playing a musical instrument, operating various vehicles, are all the same.
A final difference is the problem of the reader being alienated by lines like "I did X" when in fact they would never do X, whatever it is. At times such lines remind them they are reading in a way that "She did X" or "He did X" would not. Such lines can break reader immersion and create a mix in which sometimes the reader identifies with the MC as themselves, and sometimes is forced to not identify, and see the MC as somebody speaking to them. Whereas in 3PL, it is consistent and always "She did X", the reader is always the invisible observer, and the narrator basically disappears.
I believe most novels are written in 3P or 3PL for a good reason, it is because of the greater leeway it provides you as an author, that slight distance from the MC is useful. I think you will have an easier road to success if you do the same.