Yep, I found the `shell.nix` setup to be too complicated and time consuming, even if it's technically "correct", so I just `nix-env -iA nixpkgs.pkg_name` every time I would have previously used `brew install pkg_name`. Since nix isolates each package from every other package, there's no risk of package incompatibilities when I do this (compare to homebrew, where package A needs one version of python and package B needs another version, and updating python can break both...), and so every project I work on just has all the tools it'll ever need.

For package management within a project, I just whatever tool is appropriate for the language -- NPM, Poetry, Cargo, etc.