NAT, when done on the carrier level (CGNAT), more or less prevents external systems from initating connections with anything on your network (without ISP involvement). You can still initiate outgoing connections fine.

Sounds great for security, but this enforces the existence of centralized services (middlemen) that you have to use/pay for if you want to have asynchronous communication with anyone that you might not necessarily initiate.

If you want a chance at a real decentralized Internet without dependency on tech giants, you're gonna need IPv6.

One of the vexing things about IPv4 (which is not really fixed by IPv6) is that endpoint devices are connected to the network but not really part of the network: there are different sets of protocols for connectivity within the network, and at the edge of the network. So an edge device (your phone, your VM host) can’t easily extend the network to more downstream systems (tethered devices, VMs) without hacks that hide the cluster from the network so the whole thing still appears to be a single device.

Nowadays, most clients, especially browsers, will try IPv4 and IPv6 concurrently and use the connection that comes back with an ack first. This prevents hangs at the expense of a little higher server resource usage.

But the myth of "IPv6 makes things hang randomly" remains.