I agree that direct debate is a waste of time in these situations, and I as understand, research shows only makes the flat-earther more adamant. In situations like this, I focus on trying to understand what the emotional underlying driver is that moves people to support these kinds of views and see if I can engage with that. Humans are not primarily logical. Our views are heavily driven by need for acceptance by our community or to rationalize our uniqueness/importance, both which relate back to our survival