In my personal M1, I have another NH-U9S with two Noctua NF-A9 PWM blowing to the rear and two Phanteks PH-F120MP fans exhausting under my Asus Strix 1080ti (fans and shroud removed) with another PH-F120MP mounted as intake on the vented panel.
I'm not too familiar with the Gigabyte 2080 but if it is 2.5 slot and the shroud and fans can be easily removed, I highly recommend mounting 25mm fans in exhaust under the GPU to keep the heat from rising into the CPU. Another option would be an aftermarket GPU heat sink like the Accelero III or Raijintek Morpheus II, again with fans underneath exhausting. In general this case can intake fresh air passively much better than it can exhaust heat passively, so a higher amount of exhaust flow is better for temps all around.
With intake from below the GPU, I think the ideal orientation is 92mm intake from the rear (or mounted on the U9S), a second 92mm fan mounted in pull on the front of the U9S, and 120mm exhaust fan on the vented panel, if you have one. See post #27743 from M1AF on this very informative thread on Hardforum:
https://hardforum.com/threads/ncase...x-case-updates-in-first-post.1717132/page-694
As for the AM4 bracket, you will need one from specifically from Noctua for the U9S, but they can send one to you (usually free of charge, but via international shipping) if you request it from them. They are also available on Amazon for <$10 if you want it quickly.
