.pio/libdeps/lolin32/AsyncMqttClient/src/AsyncMqttClient.cpp: In member function 'AsyncMqttClient& AsyncMqttClient::setServer(const char*, const char*)':
.pio/libdeps/lolin32/AsyncMqttClient/src/AsyncMqttClient.cpp:149:1: warning: control reaches end of non-void function [-Wreturn-type]
}
^

Indeed, this method at the end does not return anything.