is that dangerous to aircraft?

Yes but not on roofs. They're so heavy.

That street's sin is not the lack of trees, but having 6 entire lanes for cars, which apparently all go in one direction. An uncrossable nightmare that only even has stores at one side!

Those nice trees take a few decades to grow, need serious pruning, will cause foundation problems next door, and increase building setbacks anyway. We also waste two entire lanes for street parking, have basically no businesses on either side anyway, and the street is still too wide. It might be urban, but it's still a car centric hellscape, just with some shade.

Please explain? Mirrors seem to reflect much more, but maybe that's another effect.

You can do both - having solar panels over a reflective white roof (like the fancy newly discovered passive radiative cooling paints) helps increase PV output by cooling the panel.

The solar panels will still absorb and radiate heat back so you won't get as much cooling as you would have just with passive radiative cooling paint, but it'd be better than just solar on a regular roof in both ways (solar output and thermally).

Thermal radiation is just EM waves, which you can reflect.

So just put the PV panels on top, and a reflective layer below.