Why does a new Mac mini's internet connection work for one user but not another?

That's like saying that because grandpa smoked and lived to a hundred it's perfectly safe to smoke.

Many people use CMM and don't notice any problems but many do.

Macs are designed to work perfectly without the aid of "cleaning" software or any other "optimiser" or "security" gubbins.

These apps often mess with things that should be left alone and do more harm than good.

The makers are preying on the unfounded fears of the public.

Anyway my main comment was with regard to the Norton app which may or may not be a VPN.

As I mentioned, 2 of my 3 minis lost internet connection completely and switching off my VPN cured it instantly. I later switched it back on and all was well.