Input level/mikrofone level can not be adjusted - always on max

I have just installed Audacity 2.3.3. on my notebook (Ubuntu 18.04) And now I am trying for hours to adjust the Inpupt level.
The microphone level cannot be adjusted. The indicator is on the far right of the scale and cannot be moved. This is also not possible via tools (German tools). I have already reinstalled the program.
I use Ubuntu.
Do you have any ideas, why this is not working?
Steffen from Germany.

That’s normal on most Linux computers. Use the microphone level control in your Desktop audio mixer (look for a loudspeaker icon to get into the sound settings).

alright, thanks a lot Mike. I was trying to find a solution for ages :wink: