Normally if you run nix search <package> it will complain about something experimental.

Assuming you read the message and understand what you are getting yourself into, follow the instructions to enable search. Alternatively, you can search on https://search.nixos.org/.

Put the following in ~/.config/nix/nix.conf

experimental-features = nix-command flakes

Now search will work but it will rebuild cache every time you search. To avoid building cache, run nix registry pin nixpkgs.

Search packages with nix search nixpkgs <package>.