It's an antiparasitic, and a pretty good one. There were some studies done that showed general anti-viral efficacy, but the catch is that you need to take absurd dosages to get those effects, dosages that verge on being dangerous. The people who rushed out to take normal dosages of ivermectin because they caught the sniffles did no harm to themselves, but it didn't help them get over the sniffles any more than placebo. (Though it probably cleaned out a bunch of parasites and made them healthier overall, but that's beside the point.) The people who read the studies and rushed out and took very large doses of ivermectin to fight the sniffles were buying raffle tickets to the Darwin Awards.
There are viruses that it might make sense to try to fight with ivermectin, but the flu ain't one. More closer to ebola than a cough.