There are several ways to map the IPv4 address space into the IPv6 address space, going right back to the first IPv6 addressing architecture RFC. Every compatibility protocol added a new one.

IPv6 added IPSEC which was backported to IPv4.

IPv6 tried to add easy renumbering, which did’t work and had to be discarded.

IPv6 added scoped addresses which are halfbaked and limited. Site-scoped addresses never worked and were discarded; link-scoped addresses are mostly used for autoconfiguration.

IPv6 added new autoconfiguration protocols instead of reusing bootp/DHCP.