"Used" is a tricky word. How often are they used?
Anti-malarials aren't part of the normal weekly regimin in the malarial parts of Africa--and chloroquine isn't as useful as it once was. The link is to a study proposing monthly doses for children. When we lived there, we took one weekly.
Also, this meta-study of regular antihelmenthics on schoolchildren implies that these are not given what I'd call very regularly. Some of the studies used quarterly doses, some bi-annually. WHO advocated annual dosing.
It would seem likely that the anti-malarials or antihelmintics are only present in sub-Saharan Africans' blood periodically--probably on an as-needed basis. It isn't obvious that even if chloroquine or ivermectin provided prophylactic protection against COVID, that the residue from months before would make any difference. Desethylchloroquine has a half-life in the bloodstream of about 4 days. I'll take that as a proxy for the oral varieties. Ivermectin, per Merck, has a half-life of about 18 hours.
Maybe they help, but the correlation doesn't seem to help prove it.
On the other hand, I heard of one clinic that somebody who came in sick with anything remotely resembling malaria was automatically given an anti-malarial, on the grounds that they probably had that too. If that protocol is widely used, there could still be a relationship.
The devil is in the details--including the details of your assumptions.