Firewall rules with IPv6 suffixes

Hello,

I use Vyos 1.4 as a router between my ISP and my home network and I was wondering how to best use it as an IPv6 firewall.

The ISP changes the prefix frequently, so I cannot really set a fixed destination address on an IPv6 firewall rule.

https://www.reddit.com/r/homelab/comments/d53j6l/are_there_any_effective_ipv6_firewalls_for_people/ does mention the ability of using an address suffix instead, but I could not set one in the related field (source). Any idea what the reddit author was talking about?