network buffering

I have 75 mbps speed wifi connected to my pc through wired but when i start stream my stream bitrate in obs is 2000-4000 kbps. Previously I streamed on 9000 kbps. This problem started 5 days ago.

I am aware that my computer's connection can be shaky sometimes. I'm not able to use ethernet so I use this extender to connect to the router, and it normally works fine, just with the occasional lag spike that leave me to wait a few seconds before the connection gets better. Unfortunately OBS...

There is a network buffer setting in OBS media source. I don't quite understand the function of the buffer. Who can answer it? thanks