So OP is correct, it does apply a measure of security. Port scanning someone behind NAT isn’t possible, you just end up port scanning their crappy NAT router provided by their ISP unless they have specifically opened up some ports and directed them to their internal IP address.
You end up just port scanning their crappy router on IPv6 as well because ports that are not opened are stuck at the firewall either way, no matter if you use IPv4 or IPv6.
Just because every device gets a public IP does not mean that IP is publicly accessible.
An advantage that IPv6 has against port scanning is the absurdly large network sizes. For example, my ISP gives me a /56 prefix, that is 4,722,366,482,869,645,213,696 IPv6 addresses. Good luck finding the used ones with the port open you need.
Even with just a /64 prefix you get 18,446,744,073,709,551,616 addresses, way outside the feasibility of port scanning.