It’s NOT IPv6 exclusive (I don’t think anyone wants to enforce that intentionally). The latest firmware includes support for dual IPv4 and IPv6. If you started from the OSPi pre-configured SD card image (which by the way was created a few years ago on an older version of Raspbian), it has problem with the latest firmware due to lack of support for dual IPv4 and IPv6. Just install the latest Raspbian and then follow the firmware installation instructions, that should make it work.