This is so subject dependent! Flowing water and birds in flight are 2 really good examples. Both need shutter speeds set to capture what you want. Flowing water changes quite a bit with different shutter speeds. If you want to freeze bird flight you need a very fast shutter speed, but to blur it a little (to convey motion) you need a slower shutter speed. In both cases, you may want various apertures depending on the DoF you want/need. And all of this applies to bright days as much as dimmer ones—it's about the subject and how you want to portray it. Hence you'd want to vary both aperture and shutter speed.
Landscapes and more static subjects may be more forgiving, but again depends on how you want to portray them. For those you'd often be fine in Av mode, but of course there are exceptions.
On my R5's, I've worked around this using C1-3 saved settings. I've set C1 to Manual with Auto ISO and C2 to Av mode with ISO I vary. When I'm shooting birds/wildlife, I switch to C1 which has fast shutter speed, "reasonable" aperture, and I adjust both as the situation warrants. The camera responds with an ISO and I pay attention, adjusting Exposure Compensation if needed. With landscapes and such, I switch to C2. Again, though, paying attention to the shutter speed the camera sets and adjusting whatever's needed to capture the shot.
As you gain experience you'll catch on to the settings you need for various subjects/settings.
