@BubbleBoy Try disable dhcp-v6-server in your router. For me this worked after I disabled it in my fritzbox. Now I have an ipv4 adress.
Now I can ssh into my device.
BUT unfortunatly there is a bug in the version 4.0.0 that don't let me connect to the internet. Hope it will be fixed soon. You can find that bug in the forum.
https://forum.recalbox.com/topic/5039/can-t-connect/1