In my story, the MC belongs to a minor nobility, and as a 13 yo kid, he isn't allowed outside his family wing after bedtime. He sneaks into other wings after midnight hoping to uncover assassination plots. There are no doors leading into wings so there's no need to figure out how to unlock them, and once he gets there, there's rarely any need for him to enter bedrooms, so that's pretty safe, too. Maybe I should just ignore it and hope readers don't think something like: "Why isn't anyone reviewing the surveillance footage?"
Auto-quoting isn't working right now so trying to do this manually.

For me, the crux of whether I'd notice the lack of surveillance comes down to your individual telling of the story. As others have said, don't emphasise what's not necessary. You say your character is running around looking for assassination plots. So this seems fairly black-and-white:

1. No-one believes these plots exist, but your character is searching regardless.
2. There is a real and present danger of these plots but no-one is taking them seriously (hence your character doing the work).
3. There is a real and present danger of these plots and your character wants to me more involved in resolving them.

In #1 and #2 you can easily just not mention surveillance. But in #3, it seems implausible that surveillance wouldn't be present. It all comes down to how you present the events - if everyone believes there's a risk, they'll take steps to cover it, and in a contemporary+ tech level that includes surveillance. But if there's no real risk, or no perception of risk, then it's much easier to just handwave and ignore the presence of security, even if in a strictly realistic scenario there would be.

As Black Prince reminds, one strategy is to have the character USE the surveillance rather than try to avoid it. If a plucky MC wants to look around a house with cameras in every room, it might be simplest to get into the security and look around through those cameras, rather than coming up with some mega-complicated stealth scenario.

One other point: you say the character "isn't allowed" to leave their wing of the building. How is that enforced? If there are guards posted there, for example, it would be inconsistent not to have guards elsewhere. The presence of physical watchmen, as Woollybear notes, is an easy way to ignore cameras. Again, while it might not be entirely realistic to have guards and not any other kind of surveillance, having some kind of visible security ticks a box that makes the situation seem more plausible. You only really need to mention multi-layered security in heist scenarios, where the impossibility of breaking in is the whole point.