ISP configured Dynamic IP is different from what websites see when I access them
Solution 1:
The 100.64.0.0/10 subnet is Shared address space
Not a valid public IP address, if you try to connect to that address from the same ISP it might work, but it is not globally routable.
The reason for this is the IPv4 shortage, so this 100. subnet is now a special case which ISPs can use internally and do NAT on, that way reducing number of IPv4 addresses they need.
You should contact your ISP and see how you would go about getting a globally routable public IP. (many still make this option available, if not consider a change of ISP)