I agree; and I wanted to mention that you don’t need NixOS which is a full distro. Nix the package manager can be installed on any Linux distro, on Macos, or on Windows with WSL. You can set up your reproducible environment by including a devenv config in your repo, or a Nix flake.
There is documentation available for flakes here: https://zero-to-nix.com/concepts/flakes/
Oh yeah, and Nix has the advantage that you don’t need containers. If you want to run a graphical app in a container it might be tricky to access the window manager on the host system. Maybe that’s why you were setting up i3? Yeah, containers are great and flexible, but they also have a variety of downsides so Nix is better ;)