IPv4 subnetting and IPv6 subnetting don't really work the same way, though. With IPv4, there are (almost?) no ISPs that are handing out class A blocks to consumers. The vast majority of consumers will get a single IP address - and then they have to use a NAT setup to create subnets on their end.

IPv6 is _dramatically_ different. Its actually possible to get a /48 or a /56 - sometimes just for free as part of general operations. That leaves 8 or 16 bits for the customer to create hundreds or thousands of subnets. Unlike with IPv4 where most customers don't get more than one IP address, you don't have to use a NAT setup if you have a /48 or a /56. Even if you only get a /64, that still leaves 64 bits to give every device its own globally routable address without having to setup NAT.

Do we need 64 bits to identify individual devices in a subnet? IDK, maybe not. but if you are doing an apples-to-apples comparison, with IPv4 you have 32 bits for global routing. With IPv6 you have somewhere between 48 and 64 bits. The remaining 64-80 bits of the IPv6 address don't have a good analog in IPv4. So, in a lot of ways, IPv6 is a lot like taking IPv4 and expanding it to something between 48 and 64 bits and then the remaining bits you can think of basically almost like extra fields to encode information that IPv4 doesn't support.