Can you try below steps in below source by using azure shell
https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-ipv4-ipv6-dual-stack-standard-load-balancer-powershell
https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-ipv4-ipv6-dual-stack-standard-load-balancer-powershell
Seems like the solution is based on using load balancer
The subnets for IPv6 must be exactly /64 in size. This ensures future compatibility should you decide to enable routing of the subnet to an on-premises network since some routers can only accept /64 IPv6 routes.
And it has some limitations
•IPv6 for Azure virtual network is available in all global Azure Commercial and US Government regions using all deployment methods.
•ExpressRoute gateways CAN be used for IPv4-only traffic in a VNET with IPv6 enabled. Support for IPv6 traffic is on our roadmap.
•VPN gateways CANNOT be used in a VNET with IPv6 enabled, either directly or peered with "UseRemoteGateway"
•The Azure platform (AKS, etc.) does not support IPv6 communication for Containers.
•IPv6 can be load balanced only to the primary network interface (NIC) on Azure VMs. Load balancing IPv6 traffic to secondary NICs is not supported.
•IPv6-only Virtual Machines or Virtual Machines Scale Sets are not supported, each NIC must include at least one IPv4 IP configuration.
•When adding IPv6 to existing IPv4 deployments, IPv6 ranges can not be added to a VNET with existing resource navigation links.
•Forward DNS for IPv6 is supported for Azure public DNS today but Reverse DNS is not yet supported.
Thanks