I did't, I just installed the map package in openwrt and it automatically configured itself as map-t and the wan6_4 interface appeared
Ok so you installed and loaded the Kernel module but you did not configured it. How do you expect it to work then? I'm really confused...
If possible I am more confused than you. Everything seems to be working correctly except the ping to ipv4 address. Any suggestion on how I should configure it?
Maybe I've missed that part?! If so, I'm sorry. Ok, recap then: DNS and web traffic etc all works?
Do you have issues only with literal IPv4 addresses and ICMP, or what happens if you connect on a literal IPv4 with TCP/IP? What happens if you fire up curl -v 1.1.1.1 from a LAN connected PC/Client?
Exactly, the only specific case that seems to have issues is icmp with literal address.
curl -v 1.1.1.1
* Trying 1.1.1.1:80...
* TCP_NODELAY set
* Connected to 1.1.1.1 (1.1.1.1) port 80 (#0)
> GET / HTTP/1.1
> Host: 1.1.1.1
> User-Agent: curl/7.68.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 301 Moved Permanently
< Server: cloudflare
< Date: Sun, 22 Dec 2024 19:31:50 GMT
< Content-Type: text/html
< Content-Length: 167
< Connection: keep-alive
< Location: https://1.1.1.1/
< CF-RAY: 8f6288d0ff69ea5a-FCO
<
<html>
<head><title>301 Moved Permanently</title></head>
<body>
<center><h1>301 Moved Permanently</h1></center>
<hr><center>cloudflare</center>
</body>
</html>
* Connection #0 to host 1.1.1.1 left intact
Here the response of curl
Then this seams for me as an issue caused by the hardware/software used by the ISP to provider customer with IPv4 Internet access.
Then back to what I said before: From IPv6-only networks with this issue (networks using NAT64 and DNS64) is to provide DNS Records for IPv4 addresses.
But as ICMP is different then TCP or UDP, or many other Protocols, we just don't know which protocols are supported by your Network/ISP.
How many possible protocols could they use? There is no way to try them all untill it works?
If you have Linux on your desktop or a server check out /etc/protocols 
Serious, I have no clue how they implemeny map-t and or other transition so it's hard to tell from the outside what works and what not.
You can also call or write your ISP and just ask....
After more reading and more testing in the end changing the MTU of the wan port to 1520 fixed the issue. Maybe someone who knows better the protocol can explain the reason.
Each encapsulation adds another "wrapper" around the existing packet. So a 1500 Byte packet gets an extra header of the size i.e. 20 Byte. This however depends on which encapsulation is used. Also the overhead differs between v4 and v6.
i'm having the same problem now with Sky and map-t.
which port did you change to 1520? i've tried changing it on the WAN device but that had no effect.