Do you use a smaller kernel build? How do you get 880mb of ram usage? The lowest i can get is 990~1010mb with the graphics. In tty its 850~950mb. Not that it matters because i have 16gbs of ram but lower number better i guess?
I was getting the same resourve usage on NixOS as well. I think I was get to more on Arch and I'm getting more on Fedora too. I think it has something to do with NixOS' packaging being quite well-optimised because you can just have better optimisiations by not having any useless services running (controlled via configuration.nix)