How Internet Proxy is working ?

Hello Community,

I am a Network Engineer and when i perform live troubleshooting with the customers i can see that they reach internet & some application like outlook and so on via a proxy configured in their web borwser , for example the proxy IP is 10.x.x.x , while the end user LAN IP is 192.168.x.x , i would like to understand how the traffic will be destined to proxy 1st before remote destination , for example user wants to reach google and google IP is 100.100.100.100 so the packet would be:-

User source IP before Natting: 192.168.x.x

User destination IP 100.100.100.100

where in the IP header the destination will be the proxy 10.x.x.x ? will there be a tunnel which has inner and outer IPs ?

Will the source IP Natting will be performed on the WAN IP of the SD-WAN Edge / Legacy Router or it will be done on the proxy server ?

Thanks in Advance :)