My router gave freedombox a DHCPv6 lease; I need a DHCPv4 lease

I have a Freedombox Pioneer that has been sitting idle for about a year-and-a-half. I just plugged it into my router, which has given it a DHCPv6 lease, I have no idea why.

I need the router to give the Freedombox a DHCPv4 lease. How can I do that?

I don’t know what to do with (or how to access) a DHCPv6 lease.
Also I can’t access the Freedombox’s web interface.

For now, I’ve disabled the IPv6 protocol in Foris → WAN → “IPv6 protocol” dropdown menu, in the hope that the router will assign the Freedombox a DHCPv4 lease.

Another question: If I go to Luci → Network → Hostnames, and add the Freedombox there, am I creating a static IP address by choosing one from the dropdown, or will this be a dynamic address?

Any suggestions welcome.