Unable to stream: Upload- & download slow down when ingame

[neutralair]

Hi! I am very new to forums and also not very tech-savvy. However, I‘ve been very interested in starting my own stream on twitch recently, primarily wanting to stream League of Legends.

I have setup a baseline of requirements and checked if my internet and PC are capable of handling a stream. At first glance, everything should work.

On speedtest.net my download speed is around 600mbit/sec and my upload ranged from 20-40 mbit/sec.
However, once I start a game, even without other players (pratice room, just by myself) my download speed drops down to 7 mbit/sec and my upload goes down to 0.2 mbit/sec, which makes it pretty much impossible to stream on twitch.
I have uploaded 2 images regarding my speedtest results.

I‘ve tried watching my own stream on separate devices and it just looks laggy. I have also tried lowering all graphics in the game. Additionally, I have tried almost everything inside OBS Streamlabs from changing my output from 1080p and 60 fps to 720p and 30fps, and I have also lowered my bitrate down from 6000 to 4500 to 3000 to 1000 and nothing seems to work either. I have also tried running OBS as an administrator (which is supposed to help) but with no luck there, either.

So, right now I am pretty much just looking everywhere for help to see if someone has had a similar experience/ problem than me
So far, no luck there either and this is the reason why I have been looking into different forums trying to find an answer.

Best wishes!