IPv6 requirement for Matter over Thread

[opal garnet]

I am confused about the IPv6 requirement for Matter over Thread.
If I simply want to set up a Matter network using ZBT-2 in HA Green and connect simple devices such as an Ikea button and a smart lock, then what do I need to do about IPv6?
Do I need to enable it in my router?
For example, in my Asus router, if this option is disabled, is it something that needs to be enabled or is it something unrelated? https://www.asus.com/support/faq/113990/
Because my network setup is a bit non-standard, and if I enable this option, the internet seems to stop working for some reason.

[cobalt snow]

That setting is for external/wan ipv6 connectivity with the internet aand your ISP, which is not needed. As long as nothing is blocking internal/Lan ipv6 connectivity. Should just work on a flat internal network without added firewall rules to block ipv6 on lan.

Can't speak to whether or not has any general internal/lan multicast blocking or enabling settings needed from asus software.