IPv4-compatible (all zeroes in front of IPv4 address) addresses are deprecated. They were intended for automatic tunneling (see RFC 1933/2893, it’s about tunneling IPv6 through IP4-only networks) which was deprecated in favour of 6to4 (RFC 3056, 2002::/16).

IPv4-mapped addresses are supported, depending on your network stack (I think for example OpenBSD doesn’t allow it for security reasons), but only to have a combined socket listening to both IPv4 and IPv6.

NAT64 is what you want I guess, but there is no requirement for a prefix (in a sense you can choose who handles the 6-to-4 translation by choosing the prefix). There is a “well-known” prefix though: 64:ff9b::/96

NAT64 is often combined with a DNS server translating A records into the corresponding AAAA records (DNS64). I don’t know whether they solved how that works together with DNSSEC though