So I have a EOS 80D and supposedly it has a max aperture of f/8.

That's incorrect. The aperture is in the lens, not the body. All Canon EF and EF-S lenses, including the one that came with your camera, have maximum apertures larger than f/8. For example, here's an 80D kit with a f/3.5-5.6 lens, meaning that the maximum aperture changes depending on focal length, but at the wide end it's an f/3.5 lens.

Your 80D will work with any EF or EF-S mount lens.

I think the source of the confusion is that the 80D can autofocus with lenses that have a maximum aperture as slow as f/8. AF systems work with the aperture wide open, and some lenses with relatively small maximum apertures, or combinations of lenses and teleconverter with small effective max apertures, prevent the AF system from working. For example, the 80D can autofocus with an EF 70-200mm f/4L and a 2x teleconverter, which increases the maximum aperture two stops to f/8.