[sidewndr46]

Spectrum here in Austin TX assigns me a /128

[ArchOversight]

If you request a prefix delegation using DHCPv6 you will get up to a /56 which you can subnet.

8 bits of subnetting means you can create up to 256 different subnets.

[wmf]

Your router may be doing something wrong because DHCPv6-PD worked fine for me on Spectrum Austin.