More studies show that ivermectin has a positive effect in covid patients. In fact, ivermectin has no effect or has only a very weak effect in certain patients.
In medicine observational studies suffer from certain problems that are hard to overcome. The biggest is that the groups are not equal. For example, smokers die younger. Covid risk increases exponentially with age. Consequently, covid will kill more people who have reached greater age as a result of not smoking. The researchers may think that they control for these factors but in reality it is very hard to do.
If you take a random article, it says smokers have greater risks from covid: https://www.renalandurologynews.com/home/departments/mens-he...
Not much evidence in either way, but before we study for reasons how smoking could protect from covid, we would like to know for sure that this is really true.