Cofigure laptop single audio port as line-in

I have an Acer Aspire A515-55 laptop that has a single TRRS audio port. I want to use it to record in stereo using Audacity from e.g. my HIFi system in order to record to digital some old cassettes. I am using a lead with a 3.5 mm TRS plug on it to connect to the HiFi system. What I get in Audacity is input to one of the stereo tracks that is very ‘fuzzy’ with just a faint sound of the music. The only input options I have in Audacity are internal mic and headset mic, so I have set it to headset mic. In Pulse Audio Volume Control there are only 2 input options - Internal Microphone or Headset Microphone.

In Windows sound settings I am presented with the option to configure the audio port as line-in, which then allows me to record in stereo in Audacity. I guess that Windows is assigning the tip and first ring of the port to line-in left and right channels, which will connect to the tip and ring of the TRS plug.

Is there some way of configuring the audio port as line-in in Opensuse? I have searched everywhere for the answer to this, but have drawn a blank. I could, of course, admit defeat and use Windows for this job, but, as a long time unix/linux user I hate to do that.

I cannot help you directly, but I faced a similar problem and hdajackretask allowed me to play with a few configurations of the audio jack.
Please see https://forums.opensuse.org/showthread.php/509661-Enable-the-subwoofer-on-Asus-N551?p=2746689#post2746689 and read the NOTES and HINTS lines.
I don’t really know if that can help with your hardware but maybe it is worth a shot.

Thank you for your response, OrsoBruno.

I checked out the link and the links within that and as a result installed hdajackretask. However the only options it gave me for the Realtek ALC255 were internal mic, internal speaker and Black Headphone Left Side. As it is the headphone part of the audio socket that I want to reconfigure to line-in, I thought the Black Headphone might provide the option I was looking for, but it only had a range of output options. There were a number of unconnected pins, so I tried overriding some of them as they had line-in as an option, but each time I applied the override I got a “tee:/sys/class/sound/hwC0D0/reconfig: Device or resource busy” message, although the hex code for that pin displayed in Konsole did change. In any case I had no new Input Devices in pauvcontrol and no new record options in Audacity. So I still feel that I am banging my head against a brick wall. I was hoping that there would be a simple trick to enable the same functionality that is available in Windows. However I guess that is not the case.