netplan configuration - add static route

I have a linux computer (Ubuntu 22.04) with 2 interfaces both on different VLAN's. One interface should be default gateway via ipv4 and the other interface should connect via ipv6.

This is my configuration

network:
   version: 2
   ethernets:
      wan:
         match:
            macaddress: fa:a1:d2:cd:8b:35
         set-name: wan
         addresses:
         - 2000:3000::d17/48
         dhcp4: false
         dhcp6: false
         accept-ra: false
      vpn:
         match:
            macaddress: fa:08:df:79:9b:b5
         set-name: vpn
         addresses:
         - 172.29.1.17/24
         dhcp4: false
         dhcp6: false
         routes:
         - to: 172.29.29.0/24
           via: 172.29.1.1
         nameservers:
            addresses:
            - 1.1.1.1



ip -6 route
2000:3000::/48 dev wan proto kernel metric 256 pref medium
fe80::/64 dev vpn proto kernel metric 256 pref medium
fe80::/64 dev wan proto kernel metric 256 pref medium


ip -6 neighbour
fe80::c6aa:bbcc:fe48:4681 dev wan lladdr aa:bb:cc:48:46:81 router STALE
2000:3000::1 dev wan lladdr aa:bb:cc:48:46:81 router STALE

The ipv6 gateway should be

ping -6 2000:3000::1
PING 2000:3000::1(2000:300::1) 56 data bytes
64 bytes from 2000:3000::1: icmp_seq=1 ttl=64 time=0.727 ms
64 bytes from 2000:3000::1: icmp_seq=2 ttl=64 time=0.278 ms

This works fine for the VPN interface but WAN ipv6 does not have a route, so I can't reach it from outside via ipv6. How can I add a route?