There are two primary ways to hide your IP address in a BitTorrent client: with a proxy server or a VPN.
Many software developers have moved away from including proxy configuration options as the technology has been overshadowed by VPNs. Transmission is no exception.
The latest version of Transmission has no built-in proxy features. It was removed after version 2.11.
The software developer took it out citing the reason: “Proxy support was not very good – we only support tracker proxies, not peer ones.”
You can still easily hide your IP and identity in Transmission with a VPN such as NordVPN by using the VPN client software they bundle with the service.
Once the client software is connected to the VPN all your online activity will be made anonymous by the VPN service, whether you use Transmission to download torrents on your Mac or simply for browsing the web.
People who prefer to use a proxy server either have to stick with Transmission 2.11 despite its limitations or switch to alternative software like µTorrent.