There are recorded beliefs in medieval Germany, for instance, that carrying or wearing an eye from a bat will make you invisible.
Homeopathy however is pure nonsense even on a fundamental scientific level.
It is unfortunate that the two get conflated.
Now, to the question "Which folk medicines have a fairly robust (or at least promising) clinical basis?", there are certainly some: ginger[0], turmeric[1], honey[2], psilocybin[3], and of course capsaicin and peppermint. Not to mention sunshine, exercise, and meditation, all of which have traditional origins.
Taking a step back though, historically, pharmaceutical drugs have often been derived from natural remedies with bases in folk remedies. The pipeline from traditional medicine -> scientific study -> molecular isolation -> synthesis and mechanized production is pretty well-trodden. Aspirin comes from willow bark, morphine comes from opium, quinine (malaria treatment) comes from cinchona bark, paclitaxel (cancer treatment) comes from yew bark.
Homeopathy is BS though, no argument there. GP really shouldn't put it in the same bucket as folk medicine (it's not even particularly old).
[0] https://pmc.ncbi.nlm.nih.gov/articles/PMC9654013/
[1] https://pubmed.ncbi.nlm.nih.gov/36804260/
> There is no compelling scientific evidence that Oscillococcinum has any effect beyond placebo.
Does not sound promising