Please be specific about your Audacity version, please see the pink panel at the top of the page. Many sites offering the latest Audacity don’t actually do so.
it seems that only the paid audio editing sites have the option for removing individual instruments.
i visited one free backing track site that offered to ‘customize track’ after downloading.
it displayed all the vox and instruments used in my chosen track which could be individually edited if required.
after editing it guided me to a payment page.
i am looking at the info you have kindly supplied.