I setup OpenVPN Client on my router and I receive VPN's IPv4 address but I still have my public IPv6 address assigend from my ISP. When I use the OpevnVPN Connect app on Windows then I got only the IPv4 address from VPN and IPv6 is disabled. Is there some workaround than disabling IPv6 completly on my router?
AFAIK, assuming that you are using RMerlin firmware, currently, when using the OpenVPN Client that's being provided by your router - IF - the IPv6 service is already running on a device that's on your LAN, the router OpenVPN Client,
does not disable your ISP IPv6 data, which is exactly what you've seen anyway and described in post above. So although you have a perfectly valid IPv4 VPN connection, you also have a IPv6 / DNS / Geo-Location "leak" at the same time.
However, if instead, you use a OpenVPN Client that's on that ^ same device, NOT the router's OpenVPN Client, the your ISP IPv6 data can easily be disabled as part of your VPN Connection.
Assuming that you want to retain your ISP's IPv6 service & data (which I do) then the only current
workaround I found that works as desired, was to disable the IPv6 on the device itself, which then, as it's running IPv4 only, will work as desired, with the router's OpenVPN Client.
I've covered this myself, in a different thread, but
this last post specifically, the content at the end of it (after the
edit marker...) gives you an up to date 'view'. Hopefully, the router's OpenVPN Client itself, will be updated in the future, so that it operates as per the 3rd party device Clients.