And doesn't forbid you from using their platform for free if you sell the keys by yourself and you can also decide to publish your game to other stores...
I also got the same feeling from that, in fact, I would go as far as to say that nixpkgs and nix-commands integration with git works quite well and is not an issue.
So the phrase the article says
"Package managers keep falling for this. And it keeps not working out"
I feel that's untrue.
The most issue I have with this really is "flakes" integration where the whole recipe folder is copied into the store (which doesn't happen with non-flakes commands), but that's a tooling problem not an intrinsic problem of using git
To be honest I don't know what to say, you can use nix in many ways, and you don't even require to know the language.
The easiest entry-point is to just use it like a package manager, you install nix (which is just a command...) and then you have available the whole set of packages which are searchable from here: https://search.nixos.org/packages
nix-shell is just to download&add programs temporary to your PATH.
I don't feel that this is harder than something like "sudo apt install -y xxxxx" but for sure more robust and portable, and doesn't require sudo.
If at some point you want to learn the language in order to create configurations or packaging software, it may require to check a lot more documentation and examples, but for this I think it's pretty straightforward and is not harder than any other package manager like aptitude, homebrew or pacman.
If you really need a portable binary that uses shared libraries I would recommend building it with nix, you get all the dependencies including dynamic linker and glibc.
Technologies: C++(up to 23), Nix, Linux Namespaces / Docker, Python, CUDA, FPGA development(xilinx) with a little bit of linux driver development, verilog, reverse engineering, Rust-curious... In general I touch a lot of stuff and learn fast :)!
The most success I had so far on doing a project where I had to work with binary data parsing is Deku in rust, I would give this a try if I have the opportunity