That is a silly assumption, like why would you assume the worst possible setup? And it would be much easier to talk to the person managing the apartment internet than having to deal with some AI chatbot that pretends to be the support at some shitty ISP.

This. Though theoretically you could do it without CGNAT, maybe some type of complex vlan arrangement? I'm not sure, I'm not a networkologist.

I do know that I just got fiber down my road from a smaller company, still a big multi state company, but not Comcast or charter big. I called them because I was worried about CGNAT for my self hosting. The salesman didn't know what I was talking about, which is disappointing but not surprising. But they forwarded me to the tech guys, who also claimed to not know what I was talking about... Which was either a downright lie, or they were idiots, either way it's very concerning.

The price was right though, $5 cheaper per month, for 10 times faster download, and 30 times faster upload. So I gave it a shot. Thankfully I'm not behind a CGNAT, yet 🤞