OpenWrt doesn't open ports by default so I think the impact is minimal, unless this can breach nftables as well. CGNAT also mitigates this as a side effect.

If you have services open on the IPv4 net however, close them immediately as a precaution.

As much as I hate to link to this site, this particular sub is very good:

https://www.reddit.com/r/openwrt/comments/1xka85h/is_the_ope...

They say 25.12-SNAPSHOT has it fixed