HorRNet have a free stereo-viewer which works in Audacity on Windows (& allegedly Mac) …
They also have an auto EQ plugin which is well worth $20 if it is as advertised, (can try before you buy).
The HoRNet Auto EQ does work in Audacity: it flattens the frequency-response …
Now on sale: 8€ for a limited period.
It works in Audacity on Windows and is available for Mac.