I'm honestly kind of surprised things like metallic microlattices, very recently discovered and having very little to no actual use are available ingame while graphene is in the same boat but not ingame.
Using some quick searches I realize graphene isn't really documented in the areas of shear modulus and specific heat. However, I could be wrong. Even if it isn't documented, could numbers be extrapolated from graphite or no? I'm certainly not an expert in any of this so I wouldn't know.
its main disadvantage as an actual material for anything is well its essentially 2 dimensional and extremely hard to produce large scale for a 1m*1m*1cm layer of graphene you would need literal km of graphene sheets stacked one on top of each other(it is pretty useful for purposes like lenses and microchips, but I don't think that is what you are talking about...)
we do have graphene derivative products in game: graphite aerogel
I was thinking more along the lines of using micrometer thick graphene 'sheets' as armor, due to graphene's immense tensile strength it would be amazing as a spall liner, moreso that things like aramid fiber if I remember correctly. There's also its amazing thermal conductivity, which could be used as backing for things like silica aerogel so that it absorbs and distributes more of the heat than just near-always vaporizing. A massive cost per unit would make anything more than a millimeter prohibitively expensive, in the order of even more than the nickel microlattice or basalt composite. And producing graphene shouldn't be a massive concern, if kilotons of fluorine-methane fuel can be produced at a sufficient rate to be used for missile salvos and drone fleets, and with 97% nuclear masses being produced at a rate of 1 mass per ship and per NTR per ~1 year. Not that it shouldn't be a concern, just thinking out loud here.
EDIT: Also, isn't graphite aerogel entirely separate from graphene-based aerogels? As far as I know, aerographene and graphene aerogel are not the same as graphite aerogel.