Do you mean aero bar as in a flat/oval cross section instead of circular? Check out the Lezyne strip drive (they make a few different models) https://ride.lezyne.com/collections/led-lights/products/1-led-21f-v304
Canyon also makes computer mounts that you can hang a flashlight underneath: https://www.canyon.com/en-us/gear/accessories/computers-and-navigation/accessories/ another person has posted some mount adapters
If you mean aero bar as in time trial or triathlon bars, you want a mount that clamps to the bar extensions, like a Bar Fly https://www.amazon.com/Bar-Fly-Trial-Garmin-Magellan/dp/B01GRHYTBK and you can hang a light underneath it.
I just got the bar fly 4TT mount
Bar Fly 4 TT- Time Trial/Tri Mount (Includes Garmin, Polar, Wahoo, Mio, Magellan, GoPro, Light) https://smile.amazon.com/dp/B01GRHYTBK/ref=cm_sw_r_fm_apa_i_Y1uNCbCDRD9FT