An HTTP proxy can change the exit address observed by a service for traffic routed through it. That is narrower than hiding every connection or making the computer anonymous.
The earlier macOS experiment used Network Preferences → Advanced → Proxies, supplied a host and port for HTTP/HTTPS proxy settings, and checked the apparent address with an IP-checking page. Those menu names describe the older interface.
Understand the boundary
A web request showing another public IP proves only something about that request’s route. It does not establish that every application uses the proxy, that DNS follows the same path, or that the proxy operator is trustworthy. Automatic proxy discovery and manually configured proxy servers are also different configuration mechanisms.
The source’s free-proxy lists and configuration screenshots are omitted rather than presented as current service recommendations. No proxy was configured or traffic routed through a third-party server for this revision.