Dr Zelenko is best known for his advocacy of the hydroxychloroquine, zinc sulfate and azithromycin treatment of covid patients. Which triggered a federal investigation causing him to close his practice. What he knows of history or conspiracies I haven't a clue.
I’d say he’s pretty accurate on the history as well as the medicine. (He saved thousands of lives personally, and many more etens of thousands by publicisinbg his protocols for other doctors to follow:
https://vladimirzelenkomd.com/treatment-protocol/
Also IIRC, the fed investigation came after he closed his practice; he was forced out of the Monroe, NY community by some who (a) were angry he spoke in pubic on the high level of covid there and (b) because others were in competition with his clinic.
The fed investigation (which AFAIK went nowhere, let me know if you know otherwise) was because Dr Jerome Corsi (of Kerry and Swift-boat fame) sent an email to Dr. Zelenko discussing covid. but misaddressed it to someone in the Justice Dept (with a similar last name) who was investigating Corsi and his relationship with Roger Stone over the Wiki leaks...so then they started looking at Dr. Zelenko.