To my knowledge, it is not necessary to enable IPv6 on your WiFi Router for Matter or Thread (but of course IPv6 needs to be enabled for your HA).
On my HA, I have set UI->Settings->System->Network:
- IPv6 to “automatic settings”,
- IPv4 I have set static address/netmask as well as gateway and dns address.
For IPv6 on HA, HA will at least have one address starting with fe80. Since you have IPv6 enabled on your WiFi Router, it most likely is broadcasting out a “Prefix” for devices on your network to use which HA will take and make another IPv6 address.
If your Matter Server is not starting, provide some logs to give a hint as to what the problem may be.