Openwrt on internal network, fixed ipv4, auto ipv6

i'm using several TP-Link Archer C7 v2 with openwrt 23.05.2 in my local network. They all have a fixed rfc1918 ipv4.

There is a fritzbox as internet router providing ipv4 and v6.

How can i enable openwrt to accept ipv6 addresses advertised from the internet router while having static ipv4 addresses ? They currently only have internal ones (fe80::*)
Btw, works fine on other fedora linux hosts having static ipv4 addresses, e.g.

ad@lnx:~$ ifconfig
br0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet  netmask  broadcast
        inet6 2a02:908:xxxx:xxxx::5  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::21b:21ff:xxxx:xxxx  prefixlen 64  scopeid 0x20<link>