I have a 2865AC running 4.5.1_BT.
My ISP is Vodafone, via Openreach on a 900Mbps FTTH connection. I have digital voice VOIP operating on a separate Grandstream /HT801.

I've always been happy using IPv4, but the need to connect some Matter devices is pushing be towards IPv6
I have tried setting the Connection type to PPP for IPv6, as suggested on Draytek's pages. The router never connects on IPv4 or IPv6.
I have tried DHCPv6 Client, that also fails to connect and puts the router in a reboot cycle, where i can't get back into the Gui until I disconnect the ONT.
I can set static IPv6 address using the routers native address and the router will boot, but no IPv6 connection is made, however the online status page does start to show Rx traffic.
I can see if i plug the supplied Vodafone router in, it acquires IPv6 config.

Can anyone suggest a IPv6 config that will work with the 2865, on Vodafone / Openreach, to at least give me a starting point?

Connection type ipv4 needs to stays ppoe
On the ipv6 tab set that to ppp

Yep - tried that.
IPv4 WAN connection stays in PPP shutdown. The router never connects in IPv4 or IPv6.
I have a ticket open with Draytek support now.