Providing text as images is not very helpful.
Note that chan_sip should not be used for new systems, except in special cases, as bugs are unlikely to be fixed and few people on the forum are still familiar with it.
Your title doesn’t make sense, as the picture shows that the VIA address is the public one.
If you getting the public address in the Via header, there are parts of your sip.conf that you have failed to provide. However, if you are behind NAT, a public address on the IP header and private address on the IP header is correct; the router should change the IP header.
nat= is not the primary control for Asterisk inside NAT. That is externip and localnets.