I believe what you have is Poa annua, or annual bluegrass.  I read in one Extension publication that it might be the worst annual weed in lawns because it is so hard to get rid of.  It‘s seeds germinate most years between Sept 1 and Oct 1, then in grows through the winter, flowers in the spring and dies around May.  As a winter annual, it shows up very well in Bermuda lawns after they go dormant in the fall.  A pre-emergent labeled for Poa should work, but manny people use a broadleaf pre-emergent and that will not work since Poa is a grass.  Killing a grass in a grass lawn is difficult and this weed produces many, many seeds in spring that can lie dormant for years. In areas without grass, as in your last photo, any nonspecific weed killer can be used.  In your lawn you could look for a grass killer that willl not harm dormant Bermuda.  I don’t know of any, but I don’t have lawn and I pull by hand the Poa that comes up in my flower beds.  I’ve attached a link with more information about the plant.

https://plants.ces.ncsu.edu/plants/poa-annua/