Help needed with nix `trusted-users` behaviour

Hi,

I opened https://github.com/NixOS/nix/issues/3873 because I’m facing a strange behaviour from nix 2.3.7, where even as I set my user to be trusted (in /etc/nix/nix.conf on multi-user installation on top of CentOS 8.1), it still is not. I would like to rule nix out of this equation if possible, but my C++ is quite non-existent, and I’m having a hard time doing this by myself.

Could anyone give this a quick check and tell me I’m most likely wrong? This would help making progress and looking at other potential sources of errors (but I’m running low on alternative probable sources of errors :))