Is there a way to force disable 'Private Window with Tor' from Brave at installation time?

So, that’s the question. I’m aware that this setting can be disabled on brave://settings/privacy, but I would like to know how to manage its deactivation with nix.

You can use the programs.chromium module to configure brave’s group policy:

config.programs.chromium = {
    extraOpts.TorDisabled = true;
    enable = true;
};

See https://support.brave.app/hc/en-us/articles/360039248271-Group-Policy for a list of options.