When external microphone selected it also records internal sound?

Ive searched everywhere and found not a single person with a similar issue:

When I use an external headset (I already tried 3 different headsets) the internal sound is getting recorded too: People in conversations Discord/Microsoft Teams/... hear themself, my music, when i watch videos and all that stuff...

I can even see the microphone level in my audio settings reacting to internal sounds when i mute my microphone directly on my headset?

Microphone level stops reacting when I turn the input level down, but then no one can hear me...