Migrating from Windows - 'stereo mix' equivalent?/input lev stuck

Linux Mint 20.2
Audacity 2.3.3 supplied with distribution
Audacity 3.0.3 installed via ‘sudo add-apt-repository ppa:ubuntuhandbook1/audacity’ and update manager (same problem)

At least 2 problems.
I can’t find an equivalent of ‘stereo mix’ which I use for recording streaming audio etc. The only input options are ‘default’ and ‘pulse’.

The input level slider is stuck at full on, so I’m not able to reduce the recording level. I can reduce it using the Pulse Audio volume control, but the sound is still horribly distorted. Also this is a very clumsy way of doing it compared with the slider. When I try to record streaming audio I just get a horrible screeching noise.

I am not very familiar with Linux yet, so please let me know what additional information you need. Here is a screenshot from the ‘sound’ program.
Audacity screenshot.png
The only input option seems to be the microphone, so maybe Linux has not picked up the sound card properly? But I’m new to Linux so I don’t know what it should look like.
Thanks for any assistance.

On most modern Linux desktops, “default” is an alias for “pulse” (both are the same).
The equivalent of “stereo mix” on Linux is the “monitor” inputs. See: https://manual.audacityteam.org/man/tutorial_recording_computer_playback_on_linux.html

Hi Steve. Thanks for these suggestions. Probably not dissimilar to what I did, following a suggestion on the LinuxMint forum and some experimentation. I will try your suggestion as per the linked page, using Pulse.

I installed Audio Recorder. This detected ‘Built-in Audio Analogue Stereo (Audio Output)’ which I suspected might be equivalent to ‘stereo mix’. I decided to try PulseAudio Volume Control to set levels,as that has the most options of any of the volume controls I’ve tried. It now lists, in its Input Devices, ‘Monitor of Built-in Audio Analogue Stereo’. Using PulseAudio to control levels I successfully recorded streaming audio with Audio Recorder.
Next, I set Monitor of Built-in Audio Analogue Stereo as ‘fallback’ in PulseAudio - I interpreted that as being a ‘default’ device. Back to Audacity, and selecting ‘Default’ as the Recording Device resulted in a recording of the streamed audio. I set the levels again using PulseAudio and got a decent recording. A bit more fiddling about with levels will probably produce something very acceptable.
I’m not sure whether I had just missed Monitor of Built-in Audio Analogue Stereo in PulseAudio or whether it actually appeared after I installed Audio Recorder.
It would be very helpful if you could fix the stuck slider at some point. Much easier than fiddling about with an external volume controller.