Great! If you can assign the delegated IPv6 "2401:xxxx:xxxx:f24a ::" block to the LAN, it partially solves the issue (you can assign only one IPv6 to your LAN interface because your ISP provides an IPv6-PD /64, leaving no room to divide it into multiple LANs or VLANs).
For the other interfaces, you just need to try relay "2401:xxxx:xxxx:9fff ::" using IPv6 relay mode based on the official documentation: https://openwrt.org/docs/guide-user/network/ipv6/configuration?s=ipv6&s=relay#ipv6_relay
By the way, you can check if your ISP provides only one IPv6-PD /64 block or if multiple blocks can be requested, e.g. two or more IPv6-PD /64 blocks .
- See details here: IPv6-PD /60 for downstream OpenWrt router after Orange Slovensko fiber - #8 by alexq
I do not have this setup anymore because I was able to obtain multiple IPv6-PD blocks and assign them to each VLAN interface, avoiding IPv6 relay mode.