the most important feature of NixOS for me is reproducibility

Reproducibility is a big topic for Guix developers and users as well, just have a look at how many times they talk about that: https://hpc.guix.info/blog/2022/07/is-reproducibility-practical/

Also correct me if I’m wrong but I think Guix goes further on reproducibility than Nix, because everything they package is from source, whereas my understanding is that a lot of Nix packages are built from binaries.

I selfhost a Miniflux instance

I use LessPass