technically this is the center, as in “halfway point between top and bottom”
what you could do is draw a few lines, from the point to the opposing “inside point”
you only need 2 of those to get a intersection where you want to place the center of the circle
(need to turn off snap-to-grid for this)
other option is to make a circle that is the outer of the points of the star
and then you can align the center of your little circle to that