Carvativir is the same as (according to Wikipedia) or derived from (according to other sites) carvacrol. From this, it took me five minutes to find evidence that we should actually investigate this and can't just dismiss Maduro as wrong: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768712/

> Carvacrol alone exhibited high antiviral activity against RV with a SI of 33, but it was less efficient than the oil for the other viruses. Thus, Mexican oregano oil and its main component, carvacrol, are able to inhibit different human and animal viruses in vitro. Specifically, the antiviral effects of Mexican oregano oil on ACVR-HHV-1 and HRSV and of carvacrol on RV justify more detailed studies.

Even just on Wikipedia, it mentions apparently well-known antimicrobial effects, which sounds like it may help with secondary pneumonia caused by COVID (so even putting aside the possibility of antiviral effects, it may help reduce some symptoms): https://en.wikipedia.org/wiki/Carvacrol#Toxicology