Infinite recursion while loading nixpkgs

Question

I'm relatively new to nix, and I'm really clueless about what is happening.

I'm getting the following while attempting to load nixpkgs:

~ % nix repl '<nixpkgs>'
warning: future versions of Nix will require using `--file` to load a file
Welcome to Nix 2.15.0. Type :? for help.

error:
       … in the left operand of the update (//) operator

         at /nix/store/sq0gp79s1kjhf6ilxfkxsqxasi5znh1c-nixpkgs/nixpkgs/lib/fixed-points.nix:69:64:

           68|   #
           69|   extends = f: rattrs: self: let super = rattrs self; in super // f self super;
             |                                                                ^
           70|

       … in the left operand of the update (//) operator

         at /nix/store/sq0gp79s1kjhf6ilxfkxsqxasi5znh1c-nixpkgs/nixpkgs/lib/fixed-points.nix:69:64:

           68|   #
           69|   extends = f: rattrs: self: let super = rattrs self; in super // f self super;
             |                                                                ^
           70|

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: infinite recursion encountered

       at «none»:0: (source not available)

This is one of many symptoms, I encountered other instances of nixpkgs-related infinite recursion (even when attempting to run darwin-rebuild switch).

I tried to reinstall nix itself from scratch, deleting the whole store. And right after a full nix reinstallation, I got the error above just trying to jump into the REPL with nixpkgs.

I know the problem is a bit generic, but I'm failing to find any possible route to a solution. Any idea?

For reference:

~ % nix --version
nix (Nix) 2.15.0

~ % uname -a
Darwin --- 22.3.0 Darwin Kernel Version 22.3.0: Thu Jan  5 20:50:21 PST 2023; root:xnu-8792.81.2~2/RELEASE_ARM64_T8112 arm64