Most times, when a question like this is asked, people's reactions are usually based on projections. Although Islam is one of the most popular religions in the world, in fact, it is the second most popular religion. There are reports that religion will grow more in terms of population, which would be about 30.5 percent of the world's total population by 2065.
If this projection is realized as predicted, it means the long reign of Christianity as the largest religious group will become a thing of the past. The reason for this is the fact that Islam is a religion that encourages men to marry more than one wife, and the highest they are allowed to marry depends on their capacity to take adequate care of them all.
This is already yielding results in this direction as Muslims are now having more children than the followers of other religions like Christianity. However, I still don't believe in this projection as they are other reports that say Christianity will continue to maintain the lead.