ULAs are generally static, almost all IPv6 unicast addresses are static though sometimes you may have "temporary" addresses via privacy extensions on hosts, tho

ULAs are generally static, almost all IPv6 unicast addresses are static though sometimes you may have "temporary" addresses via privacy extensions on hosts, those should only be for egress traffic out to the internet, intra-lan traffic should use ULAs. Your ISP can change your prefix delegation, in practice this shouldn't happen often, but if your in a situation where you need to deal with it frequently on the same network (running a service with a short lived delegation) DDNS still works for IPv6.