WiFi is inherently variable.... especially if there are other WiFi devices in the area
So if you have to use WiFi, making sure no one/nothing else is using it (not even powered on) will usually help
And yes, dropping streaming bitrate will absolutely help... but WiFi for streaming is generally a bad combination regardless (it is why Smart devices, Roku, Chromecast, Apple TV, etc all have buffers built into them)
And be careful using the phrase lag, as technically that can mean a number of different things. There is delay caused by network congestion. There are dropped frames due to PC resource issue or dropped frames due to network connection. And then there is the normal speed of light limitation (plus use of free services like YouTube/FB/Twitch/etc) that means when you live stream, the time delay (lag) until others see the content