Flies can be (and are valuable) pollinators, along with many solitary bees and wasps. We see a fly (perhaps a Green Bottle Fly, though we cannot ID it for certain) and what looks like a Sweat Bee, as they are small and often brilliantly iridescent. Here is a sample gallery of Sweat Bee species in MD: https://www.marylandbiodiversity.com/viewThumbnails.php?family=Halictidae&

Although Japanese Wood Aster (Aster ageratoides) is not native, we do not see listings of this species indicating it is invasive in our area. If you prefer, there are numerous native Aster species and their cultivars available in horticulture which make excellent late-season nectar/pollen sources for insects and other beneficial organisms. Narrowing-down the choices depends on growing conditions (light levels, soil drainage), how tall you'd like it to get, and aesthetic preferences for color, flower size, and specific bloom season (some start earlier than others, but overall, Asters are late-summer to autumn bloomers).

Miri

You're welcome!