PAC support disabled because there is no system implementation
I think you can safely ignore this one. It is kinda hard-coded in Chromium Browser Engine.
If you check Chromium sources (https://chromium.googlesource.com/chromium/src.git/+/master/net/proxy/proxy_service.cc) and see ProxyService::CreateUsingSystemProxyResolver you will find
if (!ProxyResolverFactoryForSystem::IsSupported()) { LOG(WARNING) << "PAC support disabled because there is no " "system implementation"; return CreateWithoutProxyResolver(proxy_config_service, net_log);}where ProxyResolverFactoryForSystem::IsSupported() is just returning false if you're not on Windows or MacOS
class ProxyResolverFactoryForSystem : public ProxyResolverFactory { //[...] static bool IsSupported() {#if defined(OS_WIN) || defined(OS_MACOSX) return true;#else return false;#endif }};