I am about to move into a ground-floor flat, and it has these wall vents. It's an old building

But in one of the bedrooms, they have poorly plastered over one of them, which has caused that plaster to crack and crack along the wall as it has retained moisture. Luckily, no mould!
After I remove the patching plaster or whatever they have used to cover it, if there isn't a vent there anymore, are these plates that are still available, or are they just carved into the plasterboard itself?