There have been a few studies, but the ones completed so far have shown conflicting results.
See here:
https://www.covid19treatmentguidelines.nih.gov/tables/ivermectin-data/
All the studies were small and had significant flaws. It appears ivermectin may have a small effect, and this is why these early, small, flawed studies conflict. Detecting and measuring a small effect requires a large study.
There are a number of larger, well-designed studies being conducted in several countries now (two in Japan alone). It will be interesting to see what they show when complete.
There have been many large studies in other countries, including Japan, Australia, and India. For some reason, the CDC and AMA choose to ignore them.